I have a cart that I filled up with BAC. Then assemble the pen and stick a regular insulin syringe into the end (instead of a pen tip), dial up a dose on the pen and trigger it. Then see how many units ended up in the insulin syringe. It should match whatever dose you dialed on your pen. I’ll do several tests over the whole range that the pen can do to make sure it’s accurate for small doses and larger doses. Just make sure your cart is properly purged and that the plunger is all the way to the cart before you do your test or it’ll appear to short you and won’t be an accurate test.