E-Steps Calibruler (E-Steps Calibration Jig)

I was calibrating the rotation distance (aka E-Steps) on my Ender 3 Pro and found it cumbersome to get the filament straight and mark it with reasonable accuracy. So I made this little jig. It has one groove at `20 mm` and another groove at `70 mm`.

To use this, run the filament through the channel like shown in the picture. With the side that is closer to the 20 mm groove flush against the extruder. Then use the 70 mm groove as reference to make a mark on the filament using a Sharpie or some such.

Now you can remove the jig, and extrude `50 mm` (by first sending `G91` followed by `G1 E50 F60`.

Once the extruder has stopped rotating, run the filament through the jig just like before and observe whether or not the mark that you made has arrived at the `20 mm` groove. If so, congrats! Your E-Steps are already well calibrated! You can go now.

Otherwise, make a mark on the jig corresponding to where the mark on the filament is. Then use calipers or a ruler to measure the dist