From: Chris end, You read my mind... I was going to suggest a spring arm pressing against the roll. The further the arm travels, the lower the roll. This should also take very little adjustment since you are looking for % left. Actually, since rolls all share a common spindle diameter... it would be easy to have this auto adjust for good thick rolls vs, cheap economy paper. You know the end location, so add a sensor to know when the roll has been changed. When the "new roll" sensor is tripped, take the current reading, that is max size. Now you can calculate the difference from there to empty, and relay a % left no matter what the initial thickness is. (the only time this would start to be off is on roll "reloads" of partially used rolls).... .... Nah... a simple spring arm reading resistance based off roll diameter would probably work best.