Vetta V30 Owner's Manual page 11

PROGRAMMING YOUR WHEEL SIZE
STEP 1
Once you have selected miles or kilometers, the V-30 will automatically advance to
the wheel size setting mode indicated by the four digit default number 2155.
STEP 2
The right hand digit (5) will begin flashing. Place the magnet on the wheel sensor
to advance through the digits (5,6,7...). When the digit that you want is displayed,
remove the magnet from the sensor to set your selection. The computer will
automatically advance to the next digit (5) and it will begin flashing.
STEP 3
Repeat this process until all four digits are correctly selected. The computer will
then advance into Auto Scan mode, alternately displaying the two primary
screens.