In article
s.com, Andy Dingley scribeth thus
On Jul 26, 10:30*pm, harry wrote:

The only way I can think of determining water level without a sight
glass, would be by having trycocks above and below the aimed for water
level. *

The standard way for a very long time on stationary boilers was a
wooden float on the water level, linked through a wire or cord to the
outside. As pressures were low, leakage and mis-reading due to
pressure effects weren't a problem. This was used on ships too, but
was unsuccessful on locomotives (although it was tried), owing to the
float being shaken around - it worked when stationary though.

I was told that in days of olde when the Cambridge water co built their
first reservoir up on Lime Kiln Hill they used a long pole with a flag
thereon which rose and fell depending on the water level.

An engine man some distance away used that seen via a telescope to judge
how much water to pump uphill..

And no I don't know what they did on foggy days, suppose they had a
bloke on a horse ride up there to have a butchers;!...
--
Tony Sayer