This is a filament gauge which can record how many circles the spool has turned.
The counter is designed as intermittent gear assemble. For each stage, the input gear only have one tooth, and the output gear have ten teeth and ten circle teeth (the circle teeth are used to stop the output gear rotation).
Each stage has the ratio,10:1, so the first dial plate stand for units' place(“个”), and the second dial plate stand for ten place("十"), the third dial plate stand for hundred place("百"), the fourth dial plate stand for thousand place.
For 1.75 diameter ABS filament which density is 1000kg/m3, 1kg filament with have the length of 415m. If the spool middle diameter is 155mm, 1kg filament will turn about 852 circles.(Maybe there are more accurate computing methods). So you can record the cirlces of filament to know how many filament you have used.
For each new filament, you can turn each dial plate to let the pointer point to zero, which can be called resetting. Or, you may not do this, just let it count the circles.
You may have to buy some bearings, wich MODEL are 618-5 and 61803.
The number of dial plate is 4.
The number of interval_gear_2 is 2.
The number of cursor is 4.
The number of expander is 4.
The number of spring is 2.
The number of bearing 61803 is 2.
The number of bearing 618-5 is 4 or more.
If you can edit the step file, you can modify the height of dial plates and the cursors to look more nice.

There are three gif file, which lead you to assemble the cursor, plate, gear, and the spool holder.