Porsche Boxster Owner's Manual page 153

The stored speed should only be recalled when
traffic conditions and the road surface so permit.
Switching automatic speed control
readiness off
Press button A on the automatic speed
control lever. The green readiness light in
the speedometer goes off.
When the vehicle is parked and the ignition
switched off, the memory is cleared.
Note
On upward or downward slopes, the set speed
cannot always be maintained by the automatic
speed control.
To obtain sufficient engine braking or a better
engine-speed range, therefore, you have to select
a lower gear.
151
Controls, Instruments