Surveying for the Haweswater Aqueduct

 A walk over Grey Crag and Tarn Crag from Sadgill in Longsleddale allowed me to inspect the survey stations for the Haweswater Aqueduct. You have to be able to see each station from the previous. the first one I found was on Great Howe. It's about 2 metres high. There is a lower one visible down the hill beyond the wall.

 The one on the top of Tarn Crag is about 4 metres high. My first one appears as a dot from it.

 And looking north it is just possible to pick out the one above Haweswater itself.

They must have been measuring angles and distances, The aqueduct is deep underneath and the water flows under gravity. I'd love to know how they turned these measurements above ground into tunneling data. There is interesting information here http://www.tathamhistory.org.uk/aqueduct.php