The Chopper is essentially simple, a guillotine arm with a razor blade underneath, cutting down onto a platen made from modelling mat material. It comes with a couple of mitre guides - one with 90 and 30 degree angles, the other with 45 and 60. In the first two pictures below the 30/90 guide is in use, on the 90 degree side, which is probably the most common usage - it allows you to cut linear items such as posts to a consistent length. The other mitres allow you to cut sheet material at fixed angles.
Storing the mitre which is not in use was my concern - it would be very easy to lose it. There is also a tiny envelope of spare screws, the ones which are used to hold the blades in - again, very easy to misplace. After my experiments with magnets recently, and finding how cheap they are, I hatched a cunning plan. I glued three magnets under the platen, as shown in the third picture. Then the packet of steel screws, and the steel mitre, simply lock on and sit out of sight but safe until needed. Simples.