Question: Since IPC-A-610 calls out magnification ranges, do scopes have to be calibrated/validated on a periodic basis? I never recall one being out.
Answer: The only information I can find on the web for the calibration of microscopes is for the user measuring things as opposed to looking for a larger or more close up view of the object under inspection.
This is the information I found that mention the measurement capability of various microscopes. The calibration would be to be able to measure the same or similar items and get the same results, which is not the case with inspecting of attributes.
The link is as follows: Microscope Calibration
As with any microscope, make sure the operators know how to adjust the eyepieces, so that the unit is in focus for both eyes.