Hardi HC 2500 Series Instruction Book page 22

Speed calibration
The speed transducer can be calibrated theoretically or practically.
The practical method is recommended.
Speed constant
The theoretical speed constant, units per pulse (UPP), is the distance
For example, if the wheel circumference is 2.00 m and
4 magnets are fitted, UPP is 0.5000.
Speed practical
Practical calibration of speed is done by driving a measured distance
and correcting the display so that the actual and the calculated
distances are the same.
Theoretical speed calibration should be carried out before practical
speed calibration.
Calibration should take place in the field with a half full tank and normal
working tyre pressure in order to obtain the wheel's real "working radius".
22
C A L I B R A T I O N
S p e e d C a l i b r a t i o n
S P E E D C A L I B R AT I O N
S p e e d c o n s t a n t
in metre on the circumference of the wheel between magnets.
S P E E D C O N S T A N T
S P E E D C A L I B R AT I O N
P r a c t i c a l
x x x x x U P P