What the UK Docks and the Council did not foresee when they made the side panels vertical was the width at the foot could easily be measured from Greens Place.
Sighting along each set of pillars and putting chalk marks on the railings gave exceptionally consistent results but made the downstream pillars appear wider by a couple of inches (50cm).
I’ll leave you to work that out why that is for yourself but it is to do with the fact that the railings are not square with the pillars. For the want of a theodolite I used a roofers square and a plumbline and ended up with a figure of 13.2m.
The variation from what was measured by the Council, 13.1m, is 100mm and would normally be considered by all as a non-material consideration and was caused by parallax errors which I forgot to take into account. A 5mm misalignment becomes 100mm because of the distance of Greens Place from the structure.