Hello, I have no good news. After reviewing a motherboard of a etrex 30 and compare it with a model etrex20, I have seen the 3 sensors missing in the x20 model.
Therefore, the only valid 20to30 etrex firmware to activate the elevation plot in x20 models.
Of the three missing sensors, and barometer, is perhaps, which might add.
The chip would model: MS5607-02BA01. only 8 pin solder.
This would work with firmware 20to30.
If people are interested might further information.