We have reproduced the signal tower that indicated the ships that were waiting to enter the port the draught that the bar had. It consists of a mast, a rhombus formed by cables, with four discs at the vertices and one in the centre. The disk of the top vertex has a 1 and indicates 1 metre, the one below a 2, indicates 2 metres; the one on your left indicates 0.25 metres; the one on your right marks 0.50 metres; and the one in the centre has a 4, which indicates 4 metres. With the combination of these five discs, lifting and lowering them, you can point from 0.25 m of draught to 7 metres and 75 centimetres.

You can give it a try.