I don't know what the signals look like but if the SuperMid can't accurately work with 2 pulses/rev, then couldn't you make an adapter that always doubles the number of pulses - like a dual-edge triggered one-shot that sends a pulse at both the positive going edge, and one at the negative going edge? Would that bring it into 'calibration' range? Just curious.

In that case, you'll see 1 km distance display when you drove actual 2 km and 10 km/L display for the actual 20 km/L.
SuperMID has adjustment capability, but it limits within a certain range to find out the value was not out of order caused by malfunction.

Since you're asking, do you mean your vehicle supplies 2 pulses per revolution?

Yoshi

My vehicle supplies 2 pulses per revolution. However, I will be remembering a conversion table from the units on the SuperMID, to UK MPG. So, it will make no real difference, and I will be able to see a 2km average distance instead of a 1km average (which will be useful for engine-off coasting around here (where you can do a few 100m up a hill, then a few hundred down).

I see. I think the software solution, modifying the program, will be the best.
Regarding to the fuel parameter, we have to adjust it to meet the actual fuel usage. We know a good number for the Prius, but I had no idea about your Bluebird. I did put a guess number to your SuperMID flying to UK.
So, I'm thinking I'll send you modified processor chip after you find out the correct fuel parameter including the distance pulse adjustment.

Yoshi