I am available for custom hardware/firmware development
So, what happened! well, the generator came back from the shop fully repaired; not. They had got the voltage right (by lowering the RPM) but now the Hz was 33.
I found I could get an accurate voltage and Hz reading by plugging into my Victron Multiplus and being switched from grid to Generator could see the input.
I had a frustrating email back and forth with the supplier and learned that the tolerance is 8% and my generator was way off the mark. I am in northern Europe so 230 volts and 50 Hz is our grid. so, generator at 250 volts and 33Hz is nutz.
So I was told to take it back to the shop again...... Well, I was draining out the petrol to transport the generator by taking the fuel line off the carburetor and there behind the control panel was a small protruding adjustable thing (don't know what to call it). My brain said, 'I bet that alters the voltage'. So I rigged it all up again and yes I was right. Extraordinary where I got that idea from. So I set the RPM to give me 50Hz and twiddled the knob to give me 230v or about 400v as its a three phase unit.
Once I got the Hz closer to 50 my multi meter also started to work and give me accurate readings, at 33Hz the multi meter was 300+ and all over the shop.
I emailed back the supplier and no one had any idea that there was a voltage adjuster on the Generator.
And that's that story.
It is pretty amazing how much you can learn and find out that you are quickly exceed the knowledge of the people servicing your equipment.
Put a nominal load on the geset when adjusting your voltage and frequency. And check the unloaded voltage and frequency is still within specifications.