400mm rulers i made to help keep my x-gantry level. The vertical extrusions are taller than 400mm but these still help a lot. If you want, you can stretch them to the full height of the extrusion before printing, the measurement marks will just be incorrect. You can either have these printed as stickers from a local sign shop or do what i did. Print them on regular paper, cover the front of them with clear packing tape, and then stick them on the aluminum with double sided tape. I've included both a pdf and the original adobe illustrator file so that you can edit it to your liking.