Hans Staeger op. cit. writes;
The numbering on this chronometer is odd and out of sequence. When taking over the firm from his father in June 1796, J.R. Arnold had assigned his chromometers with four digit numbers, as is shown by a series of extant chronometers dating from that time. No other watch made by J.R. Arnold is known to bear a one or two digit number.
The story becomes more interesting when one looks at John Arnold's pocket watches more closely. A watch sold at auction by Sotheby's, London on July 21, 1806, lot 325 from the estate of Alexander Aubert was signed John Arnold No.1. The description was as follows;
A big pocket chronometer in gold case, expansion escapement, gold helical spring, jeweled bearings up to fusee, mean and sidereal time indications. It was believed to have been Aubert's personal pocket chronometer and was purchased by a Mr. J. Farny for the price of 63gns. As yet pocket chronometer No. 2 made by John Arnold is unknown. There is a note at the Royal Observatory, Greenwich, noting the use of John Arnold pocket chronometer No. 2 during a North West Passage navigation and an Artic expedition in 1824. Could this have been that very chronometer?