E-step calibrator

I designed this e-step calibration tool because measuring filament with calipers alone seemed imprecise!

It is 120 mm long. It has a groove to hold 1.75 mm filament straight and markings for 10, 15, 20, 25, and 30 mm to measure the offset.

Print quality doesn't really matter, you just want to make sure the length comes out correctly.

Instructions for optimal use:
1. Place filament in calibrator groove with raised end flush with the extruder
2. Measure out 120 mm of filament by making a mark on the filament
3. Extrude 100 mm of filament on the printer
3. Place filament in calibrator groove again and mark calibrator at the position of the mark on the filament.
4a. Use calipers to measure from the raised end of the calibrator to the mark. You can hold the bottom jaw of the calipers flush against the plastic. Subtract this value from 120 mm and you have the actual length extruded.
4b. If you don't have calipers you can still easily estimate to the nearest 2 mm or use a ruler