In the beginning I bought a PLX Devices inc Air Fuel Ratio meter to help with tuning up my progressive carburettor. At the time I bought direct from the USA and $200 plus $53 postage became £200 here in the UK. It is very fast acting and I bought a version with the older Bosch 4.2 sensor as that was what they had at the time. At the time apart from lengthening the wiring with a multicore screened cable I did nothing special so I did not bother posting a howto. Then I found a resource on the PLX devices website which was a document describing the digital protocol used between the computer box in the engine bay and the multifunction dash display. And explaining how to daisy chain sensors and displays. So I made a rev counter addon but using a very old 1990's microcontroller board ( the Philips LPC2106 chip on it can be bought NOS for about £30 these days). Again I did not write it up because it was made with effectively unobtainable parts.. This worked well despite being damaged once by ignition coil flashover having to rewrite code to move pins around on the chip to bypass the damage. Then I melted the engine bay wiring and shorted the 12 volt battery voltage to the power supply of the dash display DM-6..So that stopped working and I had to make another display. This is when the interesting stuff starts.