We are using a Wild GAK-1 Gyro to determine subsurface azimuths in a tunnel. The GAK-1 we rented has a dial above the Gyro eyepiece; the manual does not show it in any picutures or refer to it in text. If it is turned all the way one way the azimuth correction is about 6 arc minutes one way if it is turned all the way the other way it is about 6 arc minutes in the opposite direction. The tech who represents the rental company says it has no effect; we don't think so. We have taped the dial fast at the midway point to observe surface and sub surface baselines. Does anyone have any experience with the use of this unknown dial on the GAK-1 Gyro?