We are approaching the end of restoration of Helsingør Hornbækbanen number 4 https://veterantoget.dk/materiel/damplokomotiver/hhb4/. One of those pesky modern requirements is that we have a speedometer. HHB 4 did not originally have one, but the Danish railways did from the turn of the 20th century. We had parts from a Danish railways G locomotive for a water speedometer. These are being installed to satisfy our requirement for a speedometer. The speedometer consists of a turbine, belt driven from a drive axle, and a water column in the cab.

GPS speedos unacceptable?

Oh they definitely are, but they just dont fit into the interior of a 1910's steam locomotive that well. The parts are approved under the government body that regulates us, and they would have continued to sit on a shelf if we didnt decide to use them, so the decision was taken of "why not!?".

The choice was made before I became the project leader, but I will admit to being an enabler after the fact. We didn't have a speed-o plate with the right speed range on it, so I copied drawings for the right one in cad and then cast the new plate off of a 3d print.