diff --git a/qspace.py b/qspace.py
index e1c33b2..81086fa 100644
--- a/qspace.py
+++ b/qspace.py
@@ -177,7 +177,7 @@ class Wavelength(Adjustable):
 
     def __init__(self, energy):
         self.energy = energy
-        assert self.energy.units == "keV" # otherwise conversion is wrong
+#        assert self.energy.units == "keV" # otherwise conversion is wrong
         super().__init__(energy.ID + "_WL", name=energy.name + " as Wavelength", units="nm")
 
     def get_current_value(self):
@@ -193,6 +193,34 @@ class Wavelength(Adjustable):
 
 
 
+class HistoryDummy(Adjustable):
+
+    def __init__(self, ID, initial_value=None, **kwargs):
+        super().__init__(ID, **kwargs)
+        self.history = [] if initial_value is None else [initial_value]
+
+    @classmethod
+    def init_from(cls, adj):
+        ID = "HD:" + adj.ID
+        initial_value = adj.get_current_value()
+        name = cls.__name__ + " for " + adj.name
+        units = adj.units
+        return cls(ID, initial_value=initial_value, name=name, units=units)
+
+    def get_current_value(self):
+        try:
+            return self.history[-1]
+        except IndexError:
+            return None
+
+    def set_target_value(self, value):
+        self.history.append(value)
+
+    def is_moving(self):
+        return False
+
+
+
 # these point to the different motors
 mu = Motor("SATES30-RIXS:MOT_SRY.VAL")
 chi = Motor("SATES30-RIXS:MOT_SRZ.VAL")