Hi Eric, the following website might be of interest to you.
http://www.eng.yale.edu/ee-labs/morse/probe/probe.htm

-------------------------------------------------------------
Eric R Snow - Fri, Feb 10 2006 12:58 pm

The display shows the square wave with 6 divisions vertical and just
over 10 divisions horizontal. Using the VAR knob in the center of the
time/div knob I can adjust the display to show exactly 10 divisions.
When this is done is the display correct? Or is it the calibration bar
that is wrong?
Thanks,
Eric