Charles Frodsham No. 3600 was entered in the Board of Admiralty chronometer trial at the Royal Observatory for 1887; it was placed 49th out of the fifty-two entered. In the published trial results it is described as having an "ordinary balance".
In the 1883 chronometer trial Nos. 3597 and 3598, both eight-day chronometers, are described as having "Charles Frodsham's three-bar compensation balance".
The possibility is, therefore, that the present balance in No. 3600 was a replacement fitted post the 1887 trial. The alternative is that the form of balance i.e. 'ordinary balance' described in the 1887 trial results is an error. Such errors in the published results of the chornometer trials, although very rare indeed, are not unknown.
To check on the possibility of such an error the results of the annual trials have been searched up-to and including the year 1900, but No. 3600 was not re-entered for any trial after 1887.
For further information on this complex balance see Vaudrey Mercer, The Frodshams, A.H.S., 1981, pp. 405, pl. 62.