Under pressure

For safety, to minimise tyre wear and to minimise fuel consumption, it is important to ensure that your tyres are inflated to the correct pressure.  However, the gauge on my pump disagrees with the reading on my old analogue pressure gauge:  the analogue gauge reads 5 or 6 pounds/sq in higher than the pump.  So I bought myself a new digital pressure gauge - cheap and cheerful, but it got good reviews for accuracy as well as convenience.  However, that reads a pound or two lower than the pump.

So what do I believe?