In 2004, Team 25 built a similar mini-arm. You can take a look at the discussion
here. We tried different programming methods which calculated the percentage error and made decisions based on that. Surprisingly we found a really simple solution to that. We we gave the potentiometer 2 ranges. If the arm was within a 15 degrees range we told it to move the arm half speed in whatever direction. Otherwise it moved full speed and stopped at 0. Feel free to contact me if you need more help with the software end of this.