You're not allowed to actually touch the screen. Some people do hold up things like a marker or the grid paper at eye level (making sure not to touch the screen!), but I think that's a really slow approach. Look into the laptop method or tether ball method if you haven't already. It seems to help some people. Remember to always start by trying to find the smallest or largest angles in each set and then do the ones in between.
Several users here have suggested this visualization method for angles. I'm quoting sskater:
"Anyone played tetherball before? No? Yea me neither. haha, but my point is that the day before my test, I was doing ARG on DAT BC and suddenly it struck me to use this method. ARG loves to use unequal lengths for angles and this works wonderfully. Imagine that the longer side of the angle is upright, perpendicular to the ground, now look at the other line, you can clearly see how high/low it is compared to its 90 degree equivalent and use it to compare with other angles. "