your wheel speed (digital speed 1) is coming from your ECU(on digital input 1), where as you also have a digital input separately on your dash which is the beacon.
So your wheel speed calibration is being done within your ECU.
You should accurately measure your tyre diameter by marking your tyre at race pressure on the car, and roll the car forward on flat ground. If you measure between the two marked points on the ground, you will know your rolling diameter, and should now use this value to adjust your ECU wheel speed calibration.
The more accurate you are here, the better your eventual calibration will be.
regards
Jamie