If you are using U40 insulin, and use U100 syringes, there is a conversion factor. Every half unit tick mark on a U100 syringe is 0.2 units of U40 insulin. So for instance, if you want to draw up 1.0 unit of U40 insulin on a U100 syringe, you need to draw up to the 2.5 mark on the U100 syringe. So divide the units on the U100 syringe by 2.5 to get the equal units of U40 insulin. Does that make sense or did I just totally ramble too much? I'm sure maybe someone else has an easier explanation...
I used the U100 syringes with U40 Prozinc to be able to micro dose since you can dose in 0.2 increments easily that way.