It's simple math, buddy. Most U-100 slin pins (there are many brands BTW) have 50 tics, which means, since they are U-100 , they are for slin that is 100IU/mL. On a 1mL slin needle, there are almost always 50 tics, which means each tic is 2IUs of slin. Also, since the pin holds 1mL, which is...