Somebody linked to this a few years back. I thought it was pretty cool.
Great use of Archimede’s principal. No matter whether each caisson has a boat in it or not as long as the water level is the same in each they weigh the same. No lifting power needed, just power to rotate the wheel.
Any time I’ve visited it, the main use seems to be carrying the tour boats up to the higher canal and back!
There’s a frequent 1/2 hour boat trip which starts almost at the lower access to the wheel, taking the boat up to the Union Canal, through a short tunnel under the Antonine Wall to a turning basin, and back again. Well worth taking!