Filament Spool Gauge

This print was designed specifically for the quick and useful prints contest.  I am always curious on how much filament I have left before I start printing, so I decided to design something that will give me an estimate on how much filament is left on my spool.  The design was inspired by the gauge that lets you know roughly how much propane you have left in your tank.  Although it is pretty simplistic in nature, I think it is super useful.  My hope is to create more detailed amounts remaining in the future.  I will also weigh my spool in the future to make sure this is fairly accurate.  It seems to work fairly well for the standard 1kg spool (Prusament).  I used the markings on the inside of the spool to help out a little.