fix(crosshair): label decimal precision is dynamically scaled with the plot zoom; API of all affected widgets adjusted; option added to PlotBase; closes #637

bec_widgets/cli/client.py

@@ -1221,6 +1221,20 @@ class Image(RPCBase):
         Set auto range for the y-axis.
         """
 
+    @property
+    @rpc_call
+    def minimal_crosshair_precision(self) -> "int":
+        """
+        Minimum decimal places for crosshair when dynamic precision is enabled.
+        """
+
+    @minimal_crosshair_precision.setter
+    @rpc_call
+    def minimal_crosshair_precision(self) -> "int":
+        """
+        Minimum decimal places for crosshair when dynamic precision is enabled.
+        """
+
     @property
     @rpc_call
     def color_map(self) -> "str":
@@ -2350,6 +2364,20 @@ class MultiWaveform(RPCBase):
         The font size of the legend font.
         """
 
+    @property
+    @rpc_call
+    def minimal_crosshair_precision(self) -> "int":
+        """
+        Minimum decimal places for crosshair when dynamic precision is enabled.
+        """
+
+    @minimal_crosshair_precision.setter
+    @rpc_call
+    def minimal_crosshair_precision(self) -> "int":
+        """
+        Minimum decimal places for crosshair when dynamic precision is enabled.
+        """
+
     @property
     @rpc_call
     def highlighted_index(self):
@@ -3315,6 +3343,20 @@ class ScatterWaveform(RPCBase):
         The font size of the legend font.
         """
 
+    @property
+    @rpc_call
+    def minimal_crosshair_precision(self) -> "int":
+        """
+        Minimum decimal places for crosshair when dynamic precision is enabled.
+        """
+
+    @minimal_crosshair_precision.setter
+    @rpc_call
+    def minimal_crosshair_precision(self) -> "int":
+        """
+        Minimum decimal places for crosshair when dynamic precision is enabled.
+        """
+
     @property
     @rpc_call
     def main_curve(self) -> "ScatterCurve":
@@ -3789,6 +3831,20 @@ class Waveform(RPCBase):
         The font size of the legend font.
         """
 
+    @property
+    @rpc_call
+    def minimal_crosshair_precision(self) -> "int":
+        """
+        Minimum decimal places for crosshair when dynamic precision is enabled.
+        """
+
+    @minimal_crosshair_precision.setter
+    @rpc_call
+    def minimal_crosshair_precision(self) -> "int":
+        """
+        Minimum decimal places for crosshair when dynamic precision is enabled.
+        """
+
     @property
     @rpc_call
     def curves(self) -> "list[Curve]":

bec_widgets/utils/crosshair.py

@@ -34,13 +34,21 @@ class Crosshair(QObject):
     coordinatesChanged2D = Signal(tuple)
     coordinatesClicked2D = Signal(tuple)
 
-    def __init__(self, plot_item: pg.PlotItem, precision: int = 3, parent=None):
+    def __init__(
+        self,
+        plot_item: pg.PlotItem,
+        precision: int | None = None,
+        *,
+        min_precision: int = 2,
+        parent=None,
+    ):
         """
         Crosshair for 1D and 2D plots.
 
         Args:
             plot_item (pyqtgraph.PlotItem): The plot item to which the crosshair will be attached.
-            precision (int, optional): Number of decimal places to round the coordinates to. Defaults to None.
+            precision (int | None, optional): Fixed number of decimal places to display. If *None*, precision is chosen dynamically from the current view range.
+            min_precision (int, optional): The lower bound (in decimal places) used when dynamic precision is enabled. Defaults to 2.
             parent (QObject, optional): Parent object for the QObject. Defaults to None.
         """
         super().__init__(parent)
@@ -48,7 +56,9 @@ class Crosshair(QObject):
         self.is_log_x = None
         self.is_derivative = None
         self.plot_item = plot_item
-        self.precision = precision
+        self._precision = precision
+        self._min_precision = max(0, int(min_precision))  # ensure non‑negative
+
         self.v_line = pg.InfiniteLine(angle=90, movable=False)
         self.v_line.skip_auto_range = True
         self.h_line = pg.InfiniteLine(angle=0, movable=False)
@@ -93,6 +103,56 @@ class Crosshair(QObject):
 
         self._connect_to_theme_change()
 
+    @property
+    def precision(self) -> int | None:
+        """Fixed number of decimals; ``None`` enables dynamic mode."""
+        return self._precision
+
+    @precision.setter
+    def precision(self, value: int | None):
+        """
+        Set the fixed number of decimals to display.
+
+        Args:
+            value(int | None): The number of decimals to display. If `None`, dynamic precision is used based on the view range.
+        """
+        self._precision = value
+
+    @property
+    def min_precision(self) -> int:
+        """Lower bound on decimals when dynamic precision is used."""
+        return self._min_precision
+
+    @min_precision.setter
+    def min_precision(self, value: int):
+        """
+        Set the lower bound on decimals when dynamic precision is used.
+
+        Args:
+            value(int): The minimum number of decimals to display. Must be non-negative.
+        """
+        self._min_precision = max(0, int(value))
+
+    def _current_precision(self) -> int:
+        """
+        Get the current precision based on the view range or fixed precision.
+        """
+        if self._precision is not None:
+            return self._precision
+
+        # Dynamically choose precision from the smaller visible span
+        view_range = self.plot_item.vb.viewRange()
+        x_span = abs(view_range[0][1] - view_range[0][0])
+        y_span = abs(view_range[1][1] - view_range[1][0])
+
+        # Ignore zero spans that can appear during initialisation
+        spans = [s for s in (x_span, y_span) if s > 0]
+        span = min(spans) if spans else 1.0
+
+        exponent = np.floor(np.log10(span))  # order of magnitude
+        decimals = max(0, int(-exponent) + 1)
+        return max(self._min_precision, decimals)
+
     def _connect_to_theme_change(self):
         """Connect to the theme change signal."""
         qapp = QApplication.instance()
@@ -324,6 +384,7 @@ class Crosshair(QObject):
                 # not sure how we got here, but just to be safe...
                 return
 
+            precision = self._current_precision()
             for item in self.items:
                 if isinstance(item, pg.PlotDataItem):
                     name = item.name() or str(id(item))
@@ -334,8 +395,8 @@ class Crosshair(QObject):
                     x_snapped_scaled, y_snapped_scaled = self.scale_emitted_coordinates(x, y)
                     coordinate_to_emit = (
                         name,
-                        round(x_snapped_scaled, self.precision),
+                        round(x_snapped_scaled, precision),
-                        round(y_snapped_scaled, self.precision),
+                        round(y_snapped_scaled, precision),
                     )
                     self.coordinatesChanged1D.emit(coordinate_to_emit)
                 elif isinstance(item, pg.ImageItem):
@@ -380,6 +441,7 @@ class Crosshair(QObject):
                 # not sure how we got here, but just to be safe...
                 return
 
+            precision = self._current_precision()
             for item in self.items:
                 if isinstance(item, pg.PlotDataItem):
                     name = item.name() or str(id(item))
@@ -391,8 +453,8 @@ class Crosshair(QObject):
                     x_snapped_scaled, y_snapped_scaled = self.scale_emitted_coordinates(x, y)
                     coordinate_to_emit = (
                         name,
-                        round(x_snapped_scaled, self.precision),
+                        round(x_snapped_scaled, precision),
-                        round(y_snapped_scaled, self.precision),
+                        round(y_snapped_scaled, precision),
                     )
                     self.coordinatesClicked1D.emit(coordinate_to_emit)
                 elif isinstance(item, pg.ImageItem):
@@ -443,7 +505,8 @@ class Crosshair(QObject):
         """
         x, y = pos
         x_scaled, y_scaled = self.scale_emitted_coordinates(x, y)
-        text = f"({x_scaled:.{self.precision}g}, {y_scaled:.{self.precision}g})"
+        precision = self._current_precision()
+        text = f"({x_scaled:.{precision}f}, {y_scaled:.{precision}f})"
         for item in self.items:
             if isinstance(item, pg.ImageItem):
                 image = item.image
@@ -452,7 +515,7 @@ class Crosshair(QObject):
                 ix = int(np.clip(x, 0, image.shape[0] - 1))
                 iy = int(np.clip(y, 0, image.shape[1] - 1))
                 intensity = image[ix, iy]
-                text += f"\nIntensity: {intensity:.{self.precision}g}"
+                text += f"\nIntensity: {intensity:.{precision}f}"
                 break
         # Update coordinate label
         self.coord_label.setText(text)

bec_widgets/widgets/plots/image/image.py

@@ -88,6 +88,8 @@ class Image(PlotBase):
         "auto_range_x.setter",
         "auto_range_y",
         "auto_range_y.setter",
+        "minimal_crosshair_precision",
+        "minimal_crosshair_precision.setter",
         # ImageView Specific Settings
         "color_map",
         "color_map.setter",

bec_widgets/widgets/plots/multi_waveform/multi_waveform.py

@@ -91,6 +91,8 @@ class MultiWaveform(PlotBase):
         "y_log.setter",
         "legend_label_size",
         "legend_label_size.setter",
+        "minimal_crosshair_precision",
+        "minimal_crosshair_precision.setter",
         # MultiWaveform Specific RPC Access
         "highlighted_index",
         "highlighted_index.setter",

bec_widgets/widgets/plots/plot_base.py

@@ -116,6 +116,7 @@ class PlotBase(BECWidget, QWidget):
         self._user_y_label = ""
         self._y_label_suffix = ""
         self._y_axis_units = ""
+        self._minimal_crosshair_precision = 3
 
         # Plot Indicator Items
         self.tick_item = BECTickItem(parent=self, plot_item=self.plot_item)
@@ -978,7 +979,9 @@ class PlotBase(BECWidget, QWidget):
     def hook_crosshair(self) -> None:
         """Hook the crosshair to all plots."""
         if self.crosshair is None:
-            self.crosshair = Crosshair(self.plot_item, precision=3)
+            self.crosshair = Crosshair(
+                self.plot_item, min_precision=self._minimal_crosshair_precision
+            )
             self.crosshair.crosshairChanged.connect(self.crosshair_position_changed)
             self.crosshair.crosshairClicked.connect(self.crosshair_position_clicked)
             self.crosshair.coordinatesChanged1D.connect(self.crosshair_coordinates_changed)
@@ -1006,6 +1009,29 @@ class PlotBase(BECWidget, QWidget):
 
         self.unhook_crosshair()
 
+    @SafeProperty(
+        int, doc="Minimum decimal places for crosshair when dynamic precision is enabled."
+    )
+    def minimal_crosshair_precision(self) -> int:
+        """
+        Minimum decimal places for crosshair when dynamic precision is enabled.
+        """
+        return self._minimal_crosshair_precision
+
+    @minimal_crosshair_precision.setter
+    def minimal_crosshair_precision(self, value: int):
+        """
+        Set the minimum decimal places for crosshair when dynamic precision is enabled.
+
+        Args:
+            value(int): The minimum decimal places to set.
+        """
+        value_int = max(0, int(value))
+        self._minimal_crosshair_precision = value_int
+        if self.crosshair is not None:
+            self.crosshair.min_precision = value_int
+        self.property_changed.emit("minimal_crosshair_precision", value_int)
+
     @SafeSlot()
     def reset(self) -> None:
         """Reset the plot widget."""

bec_widgets/widgets/plots/scatter_waveform/scatter_waveform.py

@@ -82,6 +82,8 @@ class ScatterWaveform(PlotBase):
         "y_log.setter",
         "legend_label_size",
         "legend_label_size.setter",
+        "minimal_crosshair_precision",
+        "minimal_crosshair_precision.setter",
         # Scatter Waveform Specific RPC Access
         "main_curve",
         "color_map",

bec_widgets/widgets/plots/setting_menus/axis_settings.py

@@ -60,6 +60,7 @@ class AxisSettings(SettingWidget):
             self.ui.y_grid,
             self.ui.inner_axes,
             self.ui.outer_axes,
+            self.ui.minimal_crosshair_precision,
         ]:
             WidgetIO.connect_widget_change_signal(widget, self.set_property)
 
@@ -121,6 +122,7 @@ class AxisSettings(SettingWidget):
             self.ui.y_max,
             self.ui.y_log,
             self.ui.y_grid,
+            self.ui.minimal_crosshair_precision,
         ]:
             property_name = widget.objectName()
             value = getattr(self.target_widget, property_name)
@@ -144,6 +146,7 @@ class AxisSettings(SettingWidget):
             self.ui.y_grid,
             self.ui.outer_axes,
             self.ui.inner_axes,
+            self.ui.minimal_crosshair_precision,
         ]:
             property_name = widget.objectName()
             value = WidgetIO.get_value(widget)

bec_widgets/widgets/plots/setting_menus/axis_settings_horizontal.ui

@@ -14,97 +14,6 @@
             <string>Form</string>
         </property>
         <layout class="QGridLayout" name="gridLayout">
-            <item row="1" column="0">
-                <widget class="QLabel" name="label">
-                    <property name="text">
-                        <string>Inner Axes</string>
-                    </property>
-                </widget>
-            </item>
-            <item row="1" column="1">
-                <widget class="ToggleSwitch" name="inner_axes"/>
-            </item>
-            <item row="1" column="2">
-                <widget class="QLabel" name="label_outer_axes">
-                    <property name="text">
-                        <string>Outer Axes</string>
-                    </property>
-                </widget>
-            </item>
-            <item row="1" column="3">
-                <widget class="ToggleSwitch" name="outer_axes">
-                    <property name="checked" stdset="0">
-                        <bool>false</bool>
-                    </property>
-                </widget>
-            </item>
-            <item row="2" column="0" colspan="2">
-                <widget class="QGroupBox" name="x_axis_box">
-                    <property name="title">
-                        <string>X Axis</string>
-                    </property>
-                    <layout class="QGridLayout" name="gridLayout_4">
-                        <item row="5" column="0">
-                            <widget class="QLabel" name="x_grid_label">
-                                <property name="text">
-                                    <string>Grid</string>
-                                </property>
-                            </widget>
-                        </item>
-                        <item row="3" column="2">
-                            <widget class="ToggleSwitch" name="x_log">
-                                <property name="checked" stdset="0">
-                                    <bool>false</bool>
-                                </property>
-                            </widget>
-                        </item>
-                        <item row="2" column="0">
-                            <widget class="QLabel" name="x_max_label">
-                                <property name="text">
-                                    <string>Max</string>
-                                </property>
-                            </widget>
-                        </item>
-                        <item row="5" column="2">
-                            <widget class="ToggleSwitch" name="x_grid">
-                                <property name="checked" stdset="0">
-                                    <bool>false</bool>
-                                </property>
-                            </widget>
-                        </item>
-                        <item row="3" column="0">
-                            <widget class="QLabel" name="x_scale_label">
-                                <property name="text">
-                                    <string>Log</string>
-                                </property>
-                            </widget>
-                        </item>
-                        <item row="1" column="0" colspan="2">
-                            <widget class="QLabel" name="x_min_label">
-                                <property name="text">
-                                    <string>Min</string>
-                                </property>
-                            </widget>
-                        </item>
-                        <item row="0" column="0">
-                            <widget class="QLabel" name="x_label_label">
-                                <property name="text">
-                                    <string>Label</string>
-                                </property>
-                            </widget>
-                        </item>
-                        <item row="0" column="2">
-                            <widget class="QLineEdit" name="x_label"/>
-                        </item>
-                        <item row="1" column="2">
-                            <widget class="BECSpinBox" name="x_min"/>
-                        </item>
-                        <item row="2" column="2">
-                            <widget class="BECSpinBox" name="x_max"/>
-                        </item>
-                    </layout>
-                </widget>
-            </item>
             <item row="2" column="2" colspan="2">
                 <widget class="QGroupBox" name="y_axis_box">
                     <property name="title">
@@ -179,6 +88,87 @@
                     </layout>
                 </widget>
             </item>
+            <item row="1" column="3">
+                <widget class="ToggleSwitch" name="outer_axes">
+                    <property name="checked" stdset="0">
+                        <bool>false</bool>
+                    </property>
+                </widget>
+            </item>
+            <item row="1" column="0">
+                <widget class="QLabel" name="label">
+                    <property name="text">
+                        <string>Inner Axes</string>
+                    </property>
+                </widget>
+            </item>
+            <item row="2" column="0" colspan="2">
+                <widget class="QGroupBox" name="x_axis_box">
+                    <property name="title">
+                        <string>X Axis</string>
+                    </property>
+                    <layout class="QGridLayout" name="gridLayout_4">
+                        <item row="5" column="0">
+                            <widget class="QLabel" name="x_grid_label">
+                                <property name="text">
+                                    <string>Grid</string>
+                                </property>
+                            </widget>
+                        </item>
+                        <item row="3" column="2">
+                            <widget class="ToggleSwitch" name="x_log">
+                                <property name="checked" stdset="0">
+                                    <bool>false</bool>
+                                </property>
+                            </widget>
+                        </item>
+                        <item row="2" column="0">
+                            <widget class="QLabel" name="x_max_label">
+                                <property name="text">
+                                    <string>Max</string>
+                                </property>
+                            </widget>
+                        </item>
+                        <item row="5" column="2">
+                            <widget class="ToggleSwitch" name="x_grid">
+                                <property name="checked" stdset="0">
+                                    <bool>false</bool>
+                                </property>
+                            </widget>
+                        </item>
+                        <item row="3" column="0">
+                            <widget class="QLabel" name="x_scale_label">
+                                <property name="text">
+                                    <string>Log</string>
+                                </property>
+                            </widget>
+                        </item>
+                        <item row="1" column="0" colspan="2">
+                            <widget class="QLabel" name="x_min_label">
+                                <property name="text">
+                                    <string>Min</string>
+                                </property>
+                            </widget>
+                        </item>
+                        <item row="0" column="0">
+                            <widget class="QLabel" name="x_label_label">
+                                <property name="text">
+                                    <string>Label</string>
+                                </property>
+                            </widget>
+                        </item>
+                        <item row="0" column="2">
+                            <widget class="QLineEdit" name="x_label"/>
+                        </item>
+                        <item row="1" column="2">
+                            <widget class="BECSpinBox" name="x_min"/>
+                        </item>
+                        <item row="2" column="2">
+                            <widget class="BECSpinBox" name="x_max"/>
+                        </item>
+                    </layout>
+                </widget>
+            </item>
             <item row="0" column="0" colspan="4">
                 <layout class="QHBoxLayout" name="horizontalLayout">
                     <item>
@@ -191,8 +181,41 @@
                     <item>
                         <widget class="QLineEdit" name="title"/>
                     </item>
+                    <item>
+                        <widget class="QLabel" name="label_2">
+                            <property name="text">
+                                <string>Precision</string>
+                            </property>
+                        </widget>
+                    </item>
+                    <item>
+                        <widget class="QSpinBox" name="minimal_crosshair_precision">
+                            <property name="toolTip">
+                                <string>Minimal Crosshair Precision</string>
+                            </property>
+                            <property name="alignment">
+                                <set>Qt::AlignmentFlag::AlignCenter</set>
+                            </property>
+                            <property name="maximum">
+                                <number>20</number>
+                            </property>
+                            <property name="value">
+                                <number>3</number>
+                            </property>
+                        </widget>
+                    </item>
                 </layout>
             </item>
+            <item row="1" column="2">
+                <widget class="QLabel" name="label_outer_axes">
+                    <property name="text">
+                        <string>Outer Axes</string>
+                    </property>
+                </widget>
+            </item>
+            <item row="1" column="1">
+                <widget class="ToggleSwitch" name="inner_axes"/>
+            </item>
         </layout>
     </widget>
     <customwidgets>

bec_widgets/widgets/plots/setting_menus/axis_settings_vertical.ui

@@ -6,15 +6,84 @@
             <rect>
                 <x>0</x>
                 <y>0</y>
-                <width>241</width>
+                <width>250</width>
-                <height>526</height>
+                <height>612</height>
             </rect>
         </property>
         <property name="windowTitle">
             <string>Form</string>
         </property>
-        <layout class="QGridLayout" name="gridLayout">
+        <layout class="QVBoxLayout" name="verticalLayout">
-            <item row="4" column="0" colspan="2">
+            <item>
+                <widget class="QGroupBox" name="general_box">
+                    <property name="title">
+                        <string>General</string>
+                    </property>
+                    <layout class="QGridLayout" name="gridLayout_2">
+                        <item row="4" column="0">
+                            <widget class="QLabel" name="label_outer_axes">
+                                <property name="text">
+                                    <string>Outer Axes</string>
+                                </property>
+                            </widget>
+                        </item>
+                        <item row="4" column="1">
+                            <widget class="ToggleSwitch" name="outer_axes">
+                                <property name="checked" stdset="0">
+                                    <bool>false</bool>
+                                </property>
+                            </widget>
+                        </item>
+                        <item row="1" column="1">
+                            <widget class="QLineEdit" name="title"/>
+                        </item>
+                        <item row="3" column="0">
+                            <widget class="QLabel" name="label">
+                                <property name="text">
+                                    <string>Inner Axes</string>
+                                </property>
+                            </widget>
+                        </item>
+                        <item row="1" column="0">
+                            <widget class="QLabel" name="plot_title_label">
+                                <property name="text">
+                                    <string>Plot Title</string>
+                                </property>
+                            </widget>
+                        </item>
+                        <item row="3" column="1">
+                            <widget class="ToggleSwitch" name="inner_axes"/>
+                        </item>
+                        <item row="2" column="0">
+                            <widget class="QLabel" name="label_2">
+                                <property name="toolTip">
+                                    <string>Minimal Crosshair Precision</string>
+                                </property>
+                                <property name="text">
+                                    <string>Precision</string>
+                                </property>
+                            </widget>
+                        </item>
+                        <item row="2" column="1">
+                            <widget class="QSpinBox" name="minimal_crosshair_precision">
+                                <property name="toolTip">
+                                    <string>Minimal Crosshair Precision</string>
+                                </property>
+                                <property name="alignment">
+                                    <set>Qt::AlignmentFlag::AlignCenter</set>
+                                </property>
+                                <property name="maximum">
+                                    <number>20</number>
+                                </property>
+                                <property name="value">
+                                    <number>3</number>
+                                </property>
+                            </widget>
+                        </item>
+                    </layout>
+                </widget>
+            </item>
+            <item>
                 <widget class="QGroupBox" name="x_axis_box">
                     <property name="title">
                         <string>X Axis</string>
@@ -81,28 +150,7 @@
                     </layout>
                 </widget>
             </item>
-            <item row="0" column="0" colspan="2">
+            <item>
-                <layout class="QHBoxLayout" name="horizontalLayout">
-                    <item>
-                        <widget class="QLabel" name="plot_title_label">
-                            <property name="text">
-                                <string>Plot Title</string>
-                            </property>
-                        </widget>
-                    </item>
-                    <item>
-                        <widget class="QLineEdit" name="title"/>
-                    </item>
-                </layout>
-            </item>
-            <item row="2" column="0">
-                <widget class="QLabel" name="label_outer_axes">
-                    <property name="text">
-                        <string>Outer Axes</string>
-                    </property>
-                </widget>
-            </item>
-            <item row="5" column="0" colspan="2">
                 <widget class="QGroupBox" name="y_axis_box">
                     <property name="title">
                         <string>Y Axis</string>
@@ -169,23 +217,6 @@
                     </layout>
                 </widget>
             </item>
-            <item row="2" column="1">
-                <widget class="ToggleSwitch" name="outer_axes">
-                    <property name="checked" stdset="0">
-                        <bool>false</bool>
-                    </property>
-                </widget>
-            </item>
-            <item row="1" column="0">
-                <widget class="QLabel" name="label">
-                    <property name="text">
-                        <string>Inner Axes</string>
-                    </property>
-                </widget>
-            </item>
-            <item row="1" column="1">
-                <widget class="ToggleSwitch" name="inner_axes"/>
-            </item>
         </layout>
     </widget>
     <customwidgets>

bec_widgets/widgets/plots/waveform/waveform.py

@@ -86,6 +86,8 @@ class Waveform(PlotBase):
         "y_log.setter",
         "legend_label_size",
         "legend_label_size.setter",
+        "minimal_crosshair_precision",
+        "minimal_crosshair_precision.setter",
         # Waveform Specific RPC Access
         "curves",
         "x_mode",

tests/unit_tests/test_crosshair.py

@@ -236,7 +236,7 @@ def test_update_coord_label_1D(plot_widget_with_crosshair):
     # Provide a test position
     pos = (10, 20)
     crosshair.update_coord_label(pos)
-    expected_text = f"({10:.3g}, {20:.3g})"
+    expected_text = f"({10:.3f}, {20:.3f})"
     # Verify that the coordinate label shows only the 1D coordinates (no intensity line)
     assert crosshair.coord_label.toPlainText() == expected_text
     label_pos = crosshair.coord_label.pos()
@@ -260,10 +260,54 @@ def test_update_coord_label_2D(image_widget_with_crosshair):
     ix = int(np.clip(0.5, 0, known_image.shape[0] - 1))  # 0
     iy = int(np.clip(1.2, 0, known_image.shape[1] - 1))  # 1
     intensity = known_image[ix, iy]  # Expected: 20
-    expected_text = f"({0.5:.3g}, {1.2:.3g})\nIntensity: {intensity:.3g}"
+    expected_text = f"({0.5:.3f}, {1.2:.3f})\nIntensity: {intensity:.3f}"
 
     assert crosshair.coord_label.toPlainText() == expected_text
     label_pos = crosshair.coord_label.pos()
     assert np.isclose(label_pos.x(), 0.5)
     assert np.isclose(label_pos.y(), 1.2)
     assert crosshair.coord_label.isVisible()
+
+
+def test_crosshair_precision_properties(plot_widget_with_crosshair):
+    """
+    Ensure Crosshair.precision and Crosshair.min_precision behave correctly
+    and that _current_precision() reflects changes immediately.
+    """
+    crosshair, plot_item = plot_widget_with_crosshair
+
+    assert crosshair.precision == 3
+    assert crosshair._current_precision() == 3
+
+    crosshair.precision = None
+    plot_item.vb.setXRange(0, 1_000, padding=0)
+    plot_item.vb.setYRange(0, 1_000, padding=0)
+    assert crosshair._current_precision() == crosshair.min_precision == 2  # default floor
+
+    crosshair.min_precision = 5
+    assert crosshair._current_precision() == 5
+
+    crosshair.precision = 1
+    assert crosshair._current_precision() == 1
+
+
+def test_crosshair_precision_properties_image(image_widget_with_crosshair):
+    """
+    The same precision/min_precision behaviour must apply for crosshairs attached
+    to ImageItem-based plots.
+    """
+    crosshair, plot_item = image_widget_with_crosshair
+
+    assert crosshair.precision == 3
+    assert crosshair._current_precision() == 3
+
+    crosshair.precision = None
+    plot_item.vb.setXRange(0, 1_000, padding=0)
+    plot_item.vb.setYRange(0, 1_000, padding=0)
+    assert crosshair._current_precision() == crosshair.min_precision == 2
+
+    crosshair.min_precision = 6
+    assert crosshair._current_precision() == 6
+
+    crosshair.precision = 2
+    assert crosshair._current_precision() == 2

tests/unit_tests/test_plot_base_next_gen.py

@@ -349,3 +349,39 @@ def test_enable_fps_monitor_property(qtbot, mocked_client):
 
     pb.enable_fps_monitor = False
     assert pb.fps_monitor is None
+
+
+def test_minimal_crosshair_precision_default(qtbot, mocked_client):
+    """
+    By default PlotBase should expose a floor of 3 decimals, with no crosshair yet.
+    """
+    pb = create_widget(qtbot, PlotBase, client=mocked_client)
+    assert pb.minimal_crosshair_precision == 3
+    assert pb.crosshair is None
+
+
+def test_minimal_crosshair_precision_before_hook(qtbot, mocked_client):
+    """
+    If the floor is changed before hook_crosshair(), the new crosshair must pick it up.
+    """
+    pb = create_widget(qtbot, PlotBase, client=mocked_client)
+    pb.minimal_crosshair_precision = 5
+    pb.hook_crosshair()
+    assert pb.crosshair is not None
+    assert pb.crosshair.min_precision == 5
+
+
+def test_minimal_crosshair_precision_after_hook(qtbot, mocked_client):
+    """
+    Changing the floor after the crosshair exists should update it immediately
+    and emit the property_changed signal.
+    """
+    pb = create_widget(qtbot, PlotBase, client=mocked_client)
+    pb.hook_crosshair()
+    assert pb.crosshair is not None
+
+    with qtbot.waitSignal(pb.property_changed, timeout=500) as sig:
+        pb.minimal_crosshair_precision = 1
+
+    assert sig.args == ["minimal_crosshair_precision", 1]
+    assert pb.crosshair.min_precision == 1