The manual says it uses Ground Grab. If you go to All Metal and press the Ground Grab (pinpoint button), that is computer ground balance and not manual (pumping the coil or not).
IMO, manual ground balance is adjusting the positive/negative sound coming from the detector sensing the ground, and using a plus/minus control to adjust it till it quiets down while pumping.
Usually, manual ground balance can be balanced all the way to salt (0) and Ground Grab usually only auto balances as low as 40 (or 20). This type detector would have difficulty at the salt water of the beach where the manual ground balance could better mask the salt water.
I know the Gamma has both computer and manual GB. But, from what I read, the Platinum does not. Please correct me if I'm wrong.