Practice but no instruction – Rapid Calculation Review

I was looking for an app that teaches rapid mental calculation (all in your head using no paper). This app doesn't help you learn that skill, but if you already know how to do mental math then you can practice with this app. At least it's free. Oh and the flashing numbers are kinda stressful and seem like they could give someone a seizure.
Review by Lawyer in nj on Rapid Calculation.