I was planning to keep my compass and camera in a hip belt pocket so I did an experiment to see if it might be affected. Click on the link to see the result.

Don't keep your compass near your camera

There was a surprisingly large effect - so, it's not worth risking this.

A very timely warning, Ian. I had compass go haywire in the Picos de Europa three years ago.

A clever feature of the Osprey hydration bladder is that instead of a fiddly clip it has a magnetic stowage point on the chest strap so it easily snaps into position. Unfortunately I keep my compass in a pouch attached to the shoulder strap of my rucksack, which in this case was right next to the mouthpiece clip.

On the second day I suddenly realised that the sun was in the wrong place! And even then I spent a confused half hour trying to believe the compass over the gps

I hadn't thought of the effects of camera & phone - thanks for the tip.

I experienced a similar phenomenon of the same ilk last year. Having walked from Kinlochleven by way of Loch Treig, I stopped at the railway bridge and took a glug of water and a breather. I then considered the remaining hours of daylight, and decided there was sufficient time to get up and over the Munro. I surveyed the skyline, compared it to the map, and decided which was the top I was aiming for. Then I took a bearing, just to be sure ... and the bearing to the top I had selected was NOTHING LIKE the bearing the map told me it should be if that were indeed my Munro.

This puzzled me.

I remained puzzled for some time ... but eventually it occurred to me that if you stand under a ruddy great slab of cast iron designed to carry railway trains safely overhead, this might just affect the performance of your compass ...