Just wondering what the four choices are for on my servo arm. I see three of the arms have three holes to choose from and the other arm has four holes. Also, what's the numbers represent on the top of the arm. 1,2,3 and 4? I just noticed the arm with the #1 has numbers next to the holes, 10,13,16 and 19. the other arm that has numbers next to the holes is arm #2. It has numbers 12,15 and 18. How or what do I do with picking an arm to use?