I'm a noob but here's how I do it... I draw the empty syringe back to the amount of my first dose to fill it with air. I insert into the vial, push the air in and invert the vial and draw out the dose. I withdraw the syringe, pull more air in to drain the needle and then express the extra air out without going so far as to lose any gear. Now I can draw the plunger back to fill with air and measure for my next dose. After I insert into my second vial, I turn it upside down, push the air out of the syringe through the gear and draw back the amount I need. You can see the gear travel up to the base of the needle. Change needles, prepare the syringe and shoot... Sounds complicated but is simpler than it sounds.