Dosing with calipers - BD syringes with 1U markings only

Hi folks, I'm in Australia, where the syringes avaliable only have full unit markings. I've been trying to calculate the appropriate measurements using digital calipers, but I'm finding it very difficult (I don't have enough hands!).
I had a look at the measurements for BD syringes with half unit markings, but they seem to be quite different - I think the two syringes must have different diameters.
So I'm wondering if anyone out there already has this info.
Any help or advice much appreciated!

Carolyn