filament left gauge

I am still in the process of designing this tool which will give an indication of the filament left on a reel and that is just a vague indication only. I currently have only been supplied with two types of reel one is 75mm core and the other is 85mm so the rule is marked for these two dimensions if you have other types then they will need other rules for those which is why the rule is removable.
This tool is not an accurate measure by any means so if a print calls for 20 meters of filament and this is saying you have 18 to 24 meters be wary and err on the low side.
Even when completed I will take no blame for you running out of filament part way through print.