I'm saying on a U100 syringe the barrel may be around 50mm and that
3u would be 1.5MM of movement. and very hard to maintain accuracy.
I use 30u, partly because I'm diabetic and have them, but I like that the
excursion from 0 to 30u is aroun 2inches. so much more granular
for small to very small doses it's like trying to pound a tack in with a 2lb
sledge. You'll want to dilute a LOT to gain more granularity.
400u of water maybe? would make 1/4mg the 10mark on syringe.
See what I mean?
BTW, suck air out equiv to the water going in or you'll have a mess.
If you ever refilled ink jet carts, you know what I mean.
Also if you don't prefill+freeze syringes, try to keep working vial upright in
fridge.