leiden GHS: make pressure scale a parameter

Change-Id: I75b919030950ea68a89f92e9ebe23f1d9c5893d8

frappy_psi/leidenghs.py

@@ -27,6 +27,7 @@ from frappy.errors import CommunicationFailedError
 
 P_SCALE = 2**14 / 1e4
 
+
 class IO(StringIO):
     end_of_line = '\n'
     identification = [('ID?', '0\\tGHS-2T-1T-700-CF.*')]
@@ -80,7 +81,7 @@ class Base(HasIO):
         return self.io._key_status[key - 1] == '2'
 
     def get_pressure(self, addr):
-        return float(self.io._pressure[addr]) / P_SCALE
+        return float(self.io._pressure[addr])
  
     def update_values(self):
         self.read_value()
@@ -173,9 +174,10 @@ class Pressure(Base, Readable):
 
     value = Parameter('pressure and flow values', datatype=FloatRange(unit='mbar'))
     addr = Property('address of pressure sensor', datatype=EnumType(PRESSURE_MAP))
+    scale = Parameter('scale factor from raw value', datatype=FloatRange(), default=P_SCALE)
 
     def read_value(self):
-        value = self.get_pressure(self.addr.value)
+        value = self.get_pressure(self.addr.value) / self.scale
         return value