Chief Delphi - ADXRS450 Gyroscope Not Reading 360 Degrees per Rotation

I'm calculating a gyro angle to turn to based on the centerX of a contour, and the center of my image

Code:

if (!isTurning) {

        turn = (centerX[0] - imageCenter) * degreesPerPixel;

}

isTurning = true;

(Using the LifeCam, and a 320x240 res, degreesPerPixel = 0.18

It seems as if the ADXRS450 does not read 360 degrees per rotation. If I reset the gyro, and spin the robot 360 degrees, the value is somewhere around 320 degrees. I tried multiplying the equation above by 0.8 to compensate, and that worked alright, but it doesn't seem like the optimal solution.