Long story short, this map, made sometime between 1750-1796, has sounding measurements and I'm trying to figure out how to interpret them. I don't see any obvious key saying what the units are, but I don't speak Dutch either. I ran the subtitle at the top through Google Translate but it doesn't seem to give any information about units. There's a thing at the bottom, (maybe a cross section?) with text but I don't know what it is or what the text means. Wikipedia tells me there were a bunch of units for length used by the Dutch at the time. Do any of you know how to figure out what units these sounding measurements might be in?
The customary unit, as with English and American and other charts of the time was the fathom (Duch: Vadem ), which was 6 feet (voet). And in this case it'd be the Amsterdam foot. By that wiki page: 28.3133 cm, which means 169.88 cm for the vadem. Per what's implied in this book and a few others it seems the Dutch only used Amsterdam fathoms for depth sounding (dieplood) and not the feet of Rijnland, Utrecht, Frisia or Groningen.
This 1810 book puts it at 1.6987982 m though, although it doesn't seem likely all those digits are significant.