[AMRadio] Is there a doctor in the house?

[CL in NC]

This is not a AM related question, and have also posted this on the CCA site.  Hopefully one of you AM restorers on this site made a living repairing test equipment, and instruments -  like meter movements.  I have a 45 year old Simpson 260 that has become inaccurate, and it is not the electronics of the meter.  The meter movement is a 50ua and 250MV full scale unit.  When a known test voltage is put onto the meter terminals with no other connections, the meter is a constant 30% off to the low side, across the scale. Inject 71MV, get a 50 indication on the meter movement, inject 357MV, you get full scale 250MV.  Under a magnifier, the meter is in excellent mechanical shape, and the needle moves without binding.  So, to an instrument guy, what happened?  Please reply off list to keep the traffic to a minimum.  Thanks.

Charlie, W4MEC in NC