The C-Force Performance Platform is calibrated by placing two known masses on the platform and recording the digital reading. The lower mass should be around 10-20 kg and the upper mass between one and four body weights (e.g. 80-400 kg). Weight plates can be used but it is easier to accurately weigh humans and then have them step onto the platform.
For routine testing the platform only requires calibrating every few weeks as a check or simply weigh someone before you start a session to check. It is also important to calibrate when you move the platform. For research, best practice is to calibrate immediately before and after the testing session.