Hi Volks.

Other than the fact that miles to metric conversion frammistat is mis
calibrated....;o)

The speedo/odo pair work like this:  They share only the cable rotations.
The odo counts rotations via a gear mechanism which can be calibrated by
selecting the proper pair of gearwheels and installing them.  Palo Alto
Speedometer (they have a website) or any reputable speedo shop can perform
this service.

The speedo has a rotating magnet whose rotation speed is directly
proportional to the rotation speed of the cable.
The magnet is close to an iron disk which is balanced by a spring.  The
rotating magnet tries to rotate the disk against the force of the spring and
in the process moves the disk and the attached pointer some angular distance
which corresponds to the speed of rotation of the shaft.  This too can be
calibrated by a good speedo shop.

The result is that the speedo can be dead accurate whilst the odo is in
error or the converse or they can both be in error.  A distance per unit
time speed measurement or a GPS will get a suitably accurate speed reading
for you.  The same GPS will provide a suitably accurate distance reading.
Compare the two and you will have the error for your particular
configuration.

The two parts odo and speedo are essentially independent of each other
insofar as accuracy is concerned and each can be adjusted/calibrated
independently.

cheers,

pensioner