Emontx3 vrms wrong

Hi how do i change the emontx3 VRMS value to be the same as the emonpi?

emonpi vrms 4s 234.9
emontx3 vrms 1s 252.2

Calibrate it. There are many articles about calibration in Resources > Building Blocks. If it’s a matter of getting emonCMS to display the same numbers, you can also tweak the multipliers in emonhub.conf. A search should find many examples where that’s been discussed.

i get the science and need for calibration, are there instructions that cover 99% of UK configurations (i am off ~200 Watts on the PV display via the emontx3); or a tool/GUI that configures the device by entering a few values/variables?

There are instructions that cover 100% of calibrations worldwide, but no automated tools. If you only want to calibrate the numbers in emonCMS (and you haven’t confirmed where or how you’re actually seeing those numbers), then all you need is a means of knowing the exact value that you are measuring, a calculator and a web browser to change the multiplier. So if you’re 2.3% low, you multiply the coefficient by 1/0.977. If you’re not using emonCMS, then you need a programmer to adjust the calibration inside your emonTx. Details of your set-up rather than “the device” would let me be more specific.