A green A will appear over the satellite logo letting you know that Tilt Comp is active. If the A is red with a slash through it, it means Tilt Comp is enabled but the IMU sensor within the rover still needs to be calibrated. You may also notice your residuals flashing red until this IMU sensor is calibrated. To calibrate the IMU sensor simply move the rover rod in circular motion or walk about 30ft with the rod over your shoulder. Once the green A comes in and the red flashing stops you know that the IMU sensor has been calibrated.