John Brockbank (sen.),Free 1769. The company Brockbanks was set up with his brother Myles, d.1821, in the Old Jewry and later at 5 Cowpers Court, London, EC. They were succeeded circa 1817 by John's sons John Edward and William.
An almost identical movement is illustrated in Rees op. cit. and has Brockbank's banking device. Evidence of the device on the present chronometer can be seen from the empty holes on the top plate and on one of the balance arms.
The detent assembly is most unusual in that it has a separate adjustment for depthing the blade and horn and for adjusting the 'lights' (i.e. the relative position at the jewelled locking pallet and the escape wheel teeth to the edge of the impulse roller) and an entirely separate assembly for adjusting the relative position of the passing spring (which is of steel) to the detent blade and horn. Provision has been made in the banking block for two screws, now lacking, the heads of which would fit into circumferential grooves at the outer ends of both the detent and passing springs and which would allow for their micro-metric depthing control. Two screws are mounted, one on each side of the banking block and are the means by which the detent and passing spring are secured in position once their separate adjustments have been made
A similar form of detent having separate adjustment is fitted to the Robert Pennington chronometer No 1/430 sold in these rooms November 25 1981, lot 210.