In reply to Matt Maynard:
is this your cycle computer?
http://www.sigmasport.com/en/produkte/bikecomputer/topline_2009_wired/bc160...
on the right hand side of the page about halfway down is a 'manuals' option.
click it and download the first pdf - it is the english language one.
page 46 says:
Change the display to TRIP UP/DOWN using the MODE 2 button.
k Hold down the SET button. Display flashes.
Press RESET/MODE 2- to count upwards (+) or downwards (-).
k Confirm by pressing the SET button. Enter the starting time for
KM COUNTER +/- by pressing RESET/MODE 2, press MODE 1 to
jump to the next digit. Confirm by pressing the SET button.
SET OK appears on the display.
which looks complicated, and you probably need to look at the diagram in the manual to make sense of it, but what they are explaining is how to set the odo to whatever value you want. In your case set all the digits to zero.