Thanks Henry. I believe you are right about the 21 step wedge. I have looked at stouffer and they sell a calibrated transmission step wedge for ~$17 so I will probably go with that. There is a zero knob on the front and calibration knob on the back. I would imagine with known values it will not be too hard to figure out how to calibrate. I guess this is a pretty old unit. Hoping I did not buy another another piece of junk
Last edited by padraigm; 01-12-2013 at 12:07 AM. Click to view previous post history.