diff --git a/secop_psi/ips_mercury.py b/secop_psi/ips_mercury.py
index c245b76..84758c5 100644
--- a/secop_psi/ips_mercury.py
+++ b/secop_psi/ips_mercury.py
@@ -132,6 +132,8 @@ class SimpleField(MercuryChannel, SimpleMagfield):
 
 
 class Field(SimpleField, Magfield):
+    persistent_field = Parameter(
+        'persistent field', FloatRange(unit='$'), readonly=False)
     wait_switch_on = Parameter(
         'wait time to ensure switch is on', FloatRange(0, unit='s'), readonly=True, default=60)
     wait_switch_off = Parameter(
diff --git a/secop_psi/magfield.py b/secop_psi/magfield.py
index 2b21687..4c04136 100644
--- a/secop_psi/magfield.py
+++ b/secop_psi/magfield.py
@@ -130,8 +130,6 @@ class Magfield(SimpleMagfield):
         'persistent mode', EnumType(Mode), readonly=False, default=Mode.PERSISTENT)
     switch_heater = Parameter('switch heater', EnumType(off=OFF, on=ON),
                               readonly=False, default=0)
-    persistent_field = Parameter(
-        'persistent field', FloatRange(unit='$'), readonly=False)
     current = Parameter(
         'leads current (in units of field)', FloatRange(unit='$'))
     # TODO: time_to_target
@@ -164,7 +162,7 @@ class Magfield(SimpleMagfield):
     def doPoll(self):
         if self.__init_persistency:
             if self.__init_persistency is True:
-                self._last_target = self.persistent_field
+                self._last_target = self.value
                 self.__init_persistency = time.time() + 60
                 self.read_value()  # check for persistent field mismatch
             elif self.read_switch_heater() and self.mode != Mode.DRIVEN:
@@ -182,11 +180,11 @@ class Magfield(SimpleMagfield):
 
     def write_mode(self, value):
         self.__init_persistency = False
-        target = self.persistent_field
+        target = self.value
         func = self.start_field_change
         if value == Mode.DISABLED:
             target = 0
-            if abs(self.persistent_field) < self.tolerance:
+            if abs(self.value) < self.tolerance:
                 func = self.start_switch_off
         elif value == Mode.PERSISTENT:
             func = self.start_switch_off
@@ -206,7 +204,7 @@ class Magfield(SimpleMagfield):
 
     def on_error(self, sm):  # sm is short for statemachine
         if self.switch_heater == ON:
-            self.persistent_field = self.read_value()
+            self.read_value()
             if sm.mode != Mode.DRIVEN:
                 self.log.warning('turn switch heater off')
                 self.write_switch_heater(OFF)
@@ -215,9 +213,9 @@ class Magfield(SimpleMagfield):
     @status_code(Status.PREPARING)
     def start_field_change(self, sm):
         self.setFastPoll(True, 1.0)
-        if sm.target == self.persistent_field or (
+        if sm.target == self.value or (
                 sm.target == self._last_target and
-                abs(sm.target - self.persistent_field) <= self.tolerance):  # short cut
+                abs(sm.target - self.value) <= self.tolerance):  # short cut
             return self.check_switch_off
         if self.switch_heater == ON:
             return self.start_switch_on
@@ -237,7 +235,7 @@ class Magfield(SimpleMagfield):
         if sm.init:
             sm.stabilize_start = 0  # in case current is already at field
             self.init_progress(sm, self.current)
-        dif = abs(self.current - self.persistent_field)
+        dif = abs(self.current - self.value)
         if dif > self.tolerance:
             tdif = self.get_progress(sm, self.current)
             if tdif > self.leads_ramp_tmo:
@@ -283,7 +281,7 @@ class Magfield(SimpleMagfield):
     @status_code(Status.PREPARING)
     def wait_for_switch_on(self, sm):
         if (sm.target == self._last_target and
-                abs(sm.target - self.persistent_field) <= self.tolerance):  # short cut
+                abs(sm.target - self.value) <= self.tolerance):  # short cut
             return self.check_switch_off
         self.read_switch_heater()  # trigger switch_on/off_time
         if self.switch_heater == OFF:
@@ -309,7 +307,6 @@ class Magfield(SimpleMagfield):
 
     @status_code(Status.RAMPING)
     def ramp_to_target(self, sm):
-        self.persistent_field = self.value
         dif = abs(self.value - sm.target)
         if sm.init:
             sm.stabilize_start = 0  # in case current is already at target
@@ -328,7 +325,6 @@ class Magfield(SimpleMagfield):
 
     @status_code(Status.STABILIZING)
     def stabilize_field(self, sm):
-        self.persistent_field = self.value
         if sm.now < sm.stabilize_start + self.wait_stable_field:
             return Retry
         return self.check_switch_off
@@ -346,7 +342,6 @@ class Magfield(SimpleMagfield):
 
     @status_code(Status.FINALIZING)
     def wait_for_switch_off(self, sm):
-        self.persistent_field = self.value
         self.read_switch_heater()
         if self.switch_heater == ON:
             if sm.init:  # avoid too many states chained
@@ -377,6 +372,6 @@ class Magfield(SimpleMagfield):
             if self.get_progress(sm, self.value) > self.leads_ramp_tmo:
                 raise HardwareError('no progress')
             return Retry
-        if sm.mode == Mode.DISABLED and abs(self.persistent_field) < self.tolerance:
+        if sm.mode == Mode.DISABLED and abs(self.value) < self.tolerance:
             return self.final_status(Status.DISABLED, 'disabled')
         return self.final_status(Status.IDLE, 'persistent mode')