Opel Speedster Operation, Safety, Maintenance Manual page 20

Odometer
Records the total distance driven.
Trip odometer
Pressing the reset button located on the
right hand side of the steering column shroud
for less than one second, will zero the
setting. This button also controls the
brightness of the instrument illumination.
Further information, see page 35.
Coolant temperature gauge
The coolant temperature is displayed in the
bottom right hand corner of the display as
soon as the coolant temperature reaches
70 °C.
For physical reasons, the coolant temperature
gauge shows the coolant temperature only if
the coolant level is adequate.
During operation the system is pressurized.
The temperature may therefore rise to over
100 °C.