Direct from the manufacturer on recalibration (I recently had a unit reading ZERO salt, and I knew there was about 3000ppm in the pool):
1. Move the switch to the Auto position. If the switch is already in the
Auto or Super Chlorinate position, move it to Off then back to Auto.
2. Wait for the relay to click, then push the diagnostics button 5 times to
the instant salt level with the minus sign in front.
3. Wait for the instant salt level to stop moving lower, make sure it is
within the range of 2700-3400, then move the switch up to Super Chlorinate
then back down to Auto. This saves the instant salt level reading as the
new default which, in effect, recalibrate the unit to be able to run
normally and chlorinate the pool.
Hope this helps,
- Jeff