We returned to the secret cave in Langstrath. My friend has a watch with an altimeter in it. It detects air pressure, which decreases with height. The problem is that air pressure varies from day to day, sometimes changing during the day itself. The top photo shows the altimeter reading at the secret cave. We then took a reading lower down at a place that we knew from the map was about 190m. So the readings were all too high. A systematic error. It is possible to calibrate the altimeter to a known height and we should have done this on the way up. So if you want to know how high the secret cave is, you can do the maths. You're getting no other clues - it's a secret after all!
