Gyro autoturn help

We have a function that takes the degree(x10) we want the robot to turn to. ex. autoTurn(900) to turn 90 degrees. We are using the vex gyro to determine the angle of the robot as we are turning. There is a proportional control in the function that slows down the motor speed as we approach the desired degree.
However, we have a problem where after every turn, the actual degree the robot turns gets smaller. The first time when we input 900 the robot turns 90 degrees. but the next time we input 900, the robot turns 87 degrees and so on…
Any help will be appreciated.

I’m going to focus the discussion for this one in the thread created in the ‘Unofficial Tech Support Thread’, as I can post in both (and this will help eliminate confusion from two threads discussing the same topic).

Unofficial Reply: Gyro autoturn help