Segway PT x2 Reference Manual page 51

Green Balance Indicator lights indicate that the Segway PT is ready
to be stepped on, or that a rider is already on:
One green Balance Indicator light in the center.
The Segway PT is in Standby Mode, ready for the rider to step
on.
Five green Balance Indicator lights pulsing.
The Segway PT is in Riderless Balance Mode, ready for the rider
to step on.
Four green Balance Indicator lights rotating.
The Segway PT is in Balance Mode with a rider on.
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