The hall effect has a sensitivity of 1.35mV/G. I guess that the real working range will be about 100mV full scale. i.e. 2.5V offset +/-100mV of signal. So, with no magnetic field, the output is at 2.5V and goes more positive by about 100mV as power is applied to the coil. Then there is a change as the plate is attracted to the body of the maglock. That is what I am really interested in. The subtle change between no armature being there to the armauture being held in place. So my small signal change has to be amplified.