Would like to upgrade old firmware on my emonTx V3 device

[jvda]

FYI here the voltage measured by my smart meter and emonTx:

and for the last 12 hours:

It looks very good.
I think there is small mismatch of 3V. So emonTx seams to measure 3V less than my smart meter.

[jvda]

Here below I did a diff between voltage reported by my digital meter for phase L2 and the voltage measured by emonTx:

So it confirms that on average my digital meter is reporting 3 Volt more than emonTx for phase L2