The English "Half-chronometer"

J.W. Benson "Observatory" watch made by Tavannes and
described  as a "Half-chronometer" as was the English made
Benson "Field" watch and many others.

The English description of a watch as being a "Half-chronometer" is, perhaps, a rather grandiose name for what the Americans termed an "adjusted" watch meaning a watch adjusted for temperature as explained in this Wikipedia entry.

This does not mean that other watches will not cope adequately with changes in temperature but that the "Adjusted" or "Half-chronometer" watch has been rigorously tested at extremes of temperature and adjusted to minimise errors.

Unfortunately most good quality English watches, particularly those by Benson, Rotherham and other good makers in Coventry and London plus most imported from Switzerland before the late 1930s and signed by English resellers are not marked "adjusted" so it is only possible to establish if they are by tracking down contemporary adverts such as the following.

From a J.W. Benson Sales catalogue from the late 1930s.