Thanks orcrist, English is not my first language so I just wanna double check if i get it. According to the instruction, I should place my other fingers on the table, keep hands and arms totally relaxed, and tap with my index finger. Am I right?
I find that I can keep my arm relaxed during slow taping, but if I try to tap faster, my arm tend to flex. The more I flex my arm, the faster I can tap.