Some transparent or shiny filaments cause false error reports from the optical filament sensor meaning it has to be disabled to complete a job.
With the sensor disabled there is no early warning of jams and snagged filaments.
This tell-tale rides on top of the extruder motor and converts the slow movement of the filament into a visible rotation - a glance is enough to check the filament is still running smoothly.
Do not confuse this with a NEMA (extruder) motor rotation indicator, this checks the Bondtech gears are actually pulling filament and not slipping.
The tell-tale is intended for occasional use and can be mounted without reinserting the filament, just pause the print for a moment.
Preassemble all parts and ensure that all rotating parts are free to move and that the body is able to fold forward under its own weight. Glue the end stops to both axles and the indicator wheel to the end of the shaft, make sure all parts are still free to move.
Whenever required clip the tell-tale in place on top of the extruder motor with its arms embracing the top of the filament sensor cover and slip the filament between the sensor wheel and the guide.