one off the list as we go. it's notjust the coordinates, but the data about the routes and information the walkers might find useful that is recorded, like how steep the hills are, is it muddy, is it stoney, and even if there's angry landowners nearby. ramblers map shows the status of parts in different colours and volunteers use it to check what needs surveying. purple shows new paths yet to be audited, like the one we are standing on, and then the green shows a completed path. just looking at the map, you can see the majority of the 40,000 miles of paths still need to be audited, but if more volunteers come out and enjoy not just the walks, but the technology too, the team will only get closer to achieving their aim. now, earlier in the programme, we'd met back up with gav from the slo mo guys to film a rocket engine test at 80x slow motion — that's 2,000 frames per second. and here's how we got on.