Magic number in ADC Pi code
According to the schematic, there is a 10k--6.8k resistor divider in the circuit.

6.8k / (6.8k + 10k) = .4047619
1/.4047619 = 2.470588

Another place to look might be:

__lsb = float(0.0000078125) # default lsb value for 18 bit
7.8125e-6 * 2^18 = 2.048  // full-scale value?
5V / 2.048 = 2.441406

Or maybe some combination of those things.

Sorry I don't have time to analyze the whole datasheet, but both of those numbers are close to your magic number.

I encourage you to work through it step by step and try to get it figured out fully -- to the point where your results match within a few mV. There is going to be a right answer, and it will help if you keep track of your units (mV, LSBs, etc)

You can learn a lot about how digital systems talk to the real world!