Porsche 911 Carrera Owner's Manual page 128

The new lap is displayed on the on-board computer
and the PCM. Timing on the on-board computer and
on the PCM begins from zero. The stopwatch in the
instrument panel continues to show the total time.
126
Controls, Instruments
The on-board computer display returns to the
"Stop timing/Intermediate time" selection
after a short period.
You can stop the stopwatch or measure
another intermediate time or a new lap.
Note
PCM: If you wish to store the lap time in the
PCM, the performance display in the "Trip/Sport
display/Begin trip" menu of the PCM must be
selected.