CITROEN DS3 Handbook page 42

distance recorders
The total and trip distances are displayed for
thirty seconds when the ignition is switched off,
when the driver's door is opened and when the
vehicle is locked or unlocked.
When travelling abroad, you may
have to change the units of distance:
the display of road speed must be in
the official units (miles or km) for the
country. The change of units is done
via the screen configuration menu, with
the vehicle stationary.
Total distance recorder
It measures the total distance travelled by the
vehicle since its first registration.
Trip distance recorder
It measures the distance travelled since it was
reset to zero by the driver.
F With the ignition on, press the button until
zeros appear.