Thanks langjie - so there does seem to be some use for this meter - maximize the regenerative braking that would also reduce brake wear to a minimum. I wish they would have expanded the range on the guage for the charging zone instead of the small area they now show.
I found this over at a Prius site that seems to suggest a slow gentle braking force on the pedal seems the maximize the charging:
The amount of electrical energy capable of dissipation is limited by either the capacity of the supply system to absorb this energy or on the state of charge of the battery or capacitors. No regenerative braking effect can occur if another electric vehicle on the same supply system is not currently drawing power or if the battery or capacitors are already charged. For this reason, it is normal to also incorporate dynamic braking to absorb the excess energy.