After a couple of prints you might want to know how much filament is left on your spool. This little device helps to stabalize the spool on a digital scale (without rolling of the scale)Simply print out the part using your favourite settings. Use an infill-% of about 20%. After printing put it on your digital scales, set them to "0" and put on the filament spool. Note the weight of the unused spool on the spool label so you know what the gross weight of the spool including filament is. In my case it was 1225 grams. By weighing the filament-spool after printing a couple of other things you can always determine how much filament is used an how much should be left. In my case this was 1225 - 1054 = 171 grams used, thus left 1000 - 171 = 829 grams, enough for a lot more printing fun ;-)