Mel is Right ( as always !!! )

For a project I am developping these days ... I use a DAC to feed the Vref + of the ADC ( external ...) and GND or a fraction of Vref+ as Vref - ...

Note Vref+ is to change with atmospheric conditions ( NO, I didn't tell it's a barometer, ... nooooo ... )

just to artificially enhance the ADC resolution ...

Alain