The M-3-Global looks astonishingly like the DT 420, with the same shape, clinometer, declination adjustment and bezel. The differences lie in the base plate markings – the M-3 doesn’t have a romer scale but has more map scales plus two rather than one direction of travel arrows – and the global balanced needle. This means the compass can be used anywhere in the world and the needle will remain steady when the compass is horizontal. Compasses with ordinary needles are balanced for the latitudes in which they are sold. Move to a far off latitude and the compass needle may tip against the housing unless the compass is held at an angle. So if you’ll be using your compass in the UK and New Zealand, say, a globally balanced one would be useful. Otherwise, given the diff erence in price and the romer scale, I’d choose the DT 420.