What is the purpose of this glass grid calibration plate?

[guythatbrews]

This glass plate is 8" square with major inch divisions and minor 0.1" divisions. The nice box appears original. No markings anywhere.

I guess it is used for calibration of some sort. Does anyone know the purpose of this plate?

Thanks!

 

[CarbideBob]

Have used something very much like it for adjusting optics and to calibrate out lens distortion in machine vision systems.
Never seen one that big.
Bob

 

[guythatbrews]

Thanks Bob.

This thing is uncalibrated and I find that odd. I've searched a bit and seems a method exists to use an uncalibrated reversible grid to calibrate 2D optical systems by checking three times with different but specific grid orientation each time. You must first calibrate one axis, then use the grid.

Maybe this was the use. Maybe not.