I'm aware of the pot to adjust the speedometer but this doesn't fix the odometer.
I'm also aware of several pulse adjustment devices which could fix both the speedometer and odometer.
The problem is that the hall sensor at the final drive is a 2 wire device which does not produce enough voltage for a pulse adjuster to work with.
The amplifier board in the lunchbox boosts this signal up so that the speedometer/odometer board can then work with it.
To hook in a pulse adjuster between the amplifier and the speedo board, it seems to me that the simplest way to do this would be to remove the amplifier from the lunch box, hook it to the pulse adjuster and then feed the amplified and pulse adjusted signal into the lunchbox using the same wire (pin 22).
Inside the lunchbox, I could take the modified signal straight to the speedometer board just by jumpering the pins which used to run in and out of the amplifier
In order to know if this is feasable, I would very much like to know more about the waveform and voltage output of the speedo amplifier board. (Moto Meter 5 4401 173 00).
See the following article for more discussion of boards and signals
https://www.motobrick.com/index.php/topic,8017.msg59081.html#msg59081