First you strip down completely naked and fill up a small wash basin with water. Next you have to squat down until the tip of your penis gets wet. Stand up and wait for it to dry, use a stop watch to time how long it takes. After you have that number post back, there is a formula to figure it out from there... note: if your butt gets wet before your penis then you don't have the balls to water correctly.
I always go by weight. I just tip a pot when im checking them. You get a feel for it, shouldn't take long. Follow the signs, check it evert day if it looks dry feels light and looks like the plant might be starting to wilt a little, water it. They need water mote often as they mature and fool or the pot