When I buy fuse - and I go through a fair amount of visco - I cut some off each end, how much depending on nominal speed, burn those to confirm speed, put a piece of tape around the fuse somewhere in the middle with the speed written on it, then store it in a ziplock bag with a card saying the speed. I have pink fuse in 2 sec/in, 10 sec/in, and 1/4 sec/in, so keeping them labelled properly is critical. I get it from various suppliers when I see it, and buy a couple of hundred feet at a time.