The fault is never where you think it is. Never.

We’ve been having problems with my Air Quality sensor code not recognising a sensor properly. It’s the worst kind of problem; where mine works but the other one doesn’t.

Today we found out that the problem was that the supplier had sent a different model of sensor device. The good news is that I’ve not got a lot of extra diagnostic code in my driver that can probably notice this next time, or at least make it easier to discover. It all goes back to one of the irrefutable truths of debugging:

If what is happening is impossible it is either not impossible, or not happening.