TexOmega
·And, I cannot add to this, never ran across one, so never researched.....I do have one or two 4992B.
Below is from 1870. Clocks mostly but maybe @Bernhard J is going to like it.
Lovely movement with superb finish (unlike Swiss equivalents at the time).
The rate would be adjusted by the screw at the side of the balance cock I assume?
(and the beautiful spring would control it and the needle would indicate change of rate).