Measure out a couple of feet and weigh it. (ie: 10 ft/2 oz) Weigh the spool before you start spinning. When you have finished the spool. Weigh the finished spool subtract the weight of the spool and divide the remaining weight by your test string. It may not be 100% accurate but it should be close. Or you could just sell it by weight.
reefdiver118 t1_itrm0gs wrote
Reply to How can I measure the length of string passing through something? by Dabrush
Measure out a couple of feet and weigh it. (ie: 10 ft/2 oz) Weigh the spool before you start spinning. When you have finished the spool. Weigh the finished spool subtract the weight of the spool and divide the remaining weight by your test string. It may not be 100% accurate but it should be close. Or you could just sell it by weight.