Reference magnets are designed expressly for the checking of Hall-Effect sensing elements. Each magnet is marked with the value of flux density, in gauss, as measured by an F.W. Bell Hall Sensor.
Probe extension cables are calibrated at the factory to achieve less than 0.1% error with a specific probe. The cable will be calibrated with that probe only. Other probes, including those with the same model number, will not be in calibration with the cable.