haha very funny.

Many stupid suggestions, jokes, and overly complicated suggestions that do the job worse than what I've already come up with myself. Line counter is the way I'm going, it seems like the perfect, relatively foolproof solution.

Just for dividing up some 1000m spools of thread into smaller batches, since it is rather hard to get in this country and resellers are taking big advantage of that by selling 100m spools for more than half the price of a 1000m one imported.

Oh yes, line counters seem to have the functionality I need, seems like they're made for fishing but I am sure I could make it work for my stuff as well. Thank you for that find! Any search with thread or string length just resulted in info about programming strings and machining threads for me.

I haven't seen something like that in hardware stores here, we just have a long measuring and cutting bench.

But that formula would break whenever there is a thread with another diameter or a spool with a different length.

I would assume that somewhat high tech will be needed, if I want to spool like 20 or 50 meters and don't want to count rotations by hand. One idea I had for a lower tech solution would be to turn the bobbin being spooled onto with a hand crank with multiple gear reductions, meaning that one turn would for example equal 1 meter. However this solution would only work if I ignore the thickness of the thread already being spooled onto it.

This does sound like a relatively safe idea, now I'd just have to find a good way to count the rotations of that barrel, or ideally just give out the total spooled length directly.