Need a little help with my 201

This maybe a silly question but I have been trying to understand the Ca calibration setting. The instructions dont cover much about this function and I havent been able to find anything in here either. If someone could point me in the right direction would be great. Oh and what is the difference between Cal Zero, Cal Range and Restore.

Help… someone has to have delt with these settings and knows their detailed function.

Hi Hightlight EX with up/dpwn keys, press feft button until it says OFF, press right top button hold in, press again to save, turn on and off, sine wave gone Fred uk