People nowadays want pre-tour briefing notes on what they’re going to visit, detailed historical background. You need trench maps and important things like a corkscrew. And, most importantly, you shouldn’t be without a compass. I was standing on top of Vimy Ridge on a foggy day, pointing to the slope up which the heroic Canadians had struggled, when someone asked why the heroic Canadians had attacked from the German side. The bugger was right, I had got the Canadians attacking their own men, a compass would have helped. Sometimes you can bluff your way out of these mishaps but this wasn’t one of them.