After you add the reagent into the vial and put the cap on start shaking it grab the tester with your other hand and push the button. When your done shaking rotate the vial on its side to remove the bubbles and shoot for getting the vial back in the checker with around 30 seconds left on the timer.I am young, I get it....another peeve I have about the tester. I like to shake and shake and shake. Sometimes tester turns off. Complete buzz kill.