Rotary calibration help

I have a cloud ray roller rotary and have set the steps per revolution. When I test this by engraving a line around the entire part the two ends line up almost perfectly. The problem I am having is when I engrave a smaller image the resulting image is not the correct size.

When I engrave a 12.47 inch line it is almost perfect.

When I engrave a .5 inch line it is .08 small.

When I engrave a 2.8 inch line it is .6 small.

This seams backwards to me, I could understand if I used a small length to “calibrate” my length that even a small deviation would result in a large difference on eve scaled up, however at the longer length I am almost perfect, just a few thousands long.

Am I missing something very simple?

Thank you

Try running in metric.

You may be suffering from a loss of significant digits in calculations.

Microcontrollers work in base 2/10, not base 12 and fractions. Anything other than metric needs to be converted every time.

I will try that. Thank you.

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