Save your time. I thought I’d try this app during a free promotion. After 5 minutes I deleted it. The idea is to match the size of the object that flashes on your screen, which worked the first round. The second round I tried about 10 times, getting within 95% or better each time (dotted lines appear to show you how you did) but each time I was below 70% sometimes 0. I could not get past the second level because of this app error. Plus, as someone already mentioned, the free version still has ads.