What is it?

On the dashboard, top right corner of the Rev counter there is a swisty switch.
It slimple says 1-2.
Any ideas what it's for?

Yes I know I'm a plonker.

I think it is your FLUX capacitor switch.  

Probably something to do with the MFA, as I don't have a MFA that is a conjecture on my part.

I asked the same question myself a few weeks ago.

I've got a set of motometer MFA clocks which dont have it in an 85 cab but my spare set from an 83 tintop does.

Im sure it'll be in someones handbook, it doesnt actually seem to do anything

It's for the MFA readout, position 1 is current reading.. eg. How many miles you have done, MPG for that journey and it resets to 0 in a couple of hours when the car is parked up.
Position 2 rememberers the mileage, MPG etc, so you can see how many miles you have done in that month etc, I think it resets after 9999 miles etc.

Later cars had the switch on the wiper stalk along with the MFA button, early cars just had the MFA button on the stalk.

Cheers for that!
I'll check it out when I get home tonight.