It is actually 0.8U
So, ProZinc is a U40 insulin. Those are U100 syringes. Here is a handy-dandy chart for using U40 insulin in a U100 syringe:
https://www.felinediabetes.com/insulin-conversions.htm
The markings on your syringes are in whole units, so each line you see is equivalent to 1 unit of U100 insulin. You are drawing up to the 2U line on a U100 syringe, which means you are actually giving 0.8U of a U40 insulin like ProZinc (thank your vet for that head scratcher).
So what you need to do is take a reduction. We normally reduce by 0.25U any time they go under 90, while you're still getting the hang of things. But since youre using U100 syringes, it is easier to decrease by 0.2U.
So, you will actually be giving 0.6U of ProZinc - and in order to do this, draw up to 1.5U on the syringes you have. This is halfway between the 1 and 2U lines on your syringes.
When you get a chance, please add "Using U100 syringes" to your signature.