Hi!
Does anyone know of any yardage counters to measure how much yarn is left on a skein?
Most of the skeins I would be measuring have several hundred yds, so I wouldn’t want to count them myself!
I’ve always imagined this arcade ticket counter style machine that you just insert the yarn in, and have it print out a receipt of how much yarn you have. 
Thanks in advance!
I love your idea of the yarn arcade machine but you’re likely breaking new ground here. If you have the yarn label and a kitchen scale, you can convert gms to yards. That’s what I usually do.
Use a Digital Scale to measure the remaining Mass of yarn. Then it is simple division and multiplication.
(Note: you can use ounces instead if grams or meters instead of yards.)
R is the total grams in the full skein.
r’ is the grams in the remainder of the skein.
Divide the remaining grams, r’, by the grams in a full skein, R and then multiply by the yards in the full skein to find the yards remaining.
If the remainder of the skein is half the grams (or ounces) of the full skein then you will also have half the yardage.
Wow, it took me more than 22 minutes longer (and many more words) to type the same message as @salmonmac
But so much better detail!