cylinders made of ruby. Arnold made another watch for the King around 1768, which was a gold and enamel pair cased watch with a movement that had every refinement, including minute repetition and centre seconds motion. In addition, Arnold fitted bi-metallic temperature compensation, and not only was every pivot hole jewelled but the escapement also had a stone cylinder made of ruby or sapphire. Arnold designated this watch "Number 1", as he did with all watches he made that he regarded as significant, these numbering twenty in all. Other early productions by Arnold from 1768 to 1770 display both originality and ingenuity; this includes a centre seconds watch wound up by depressing the pendant once a day. The movement of this watch was also fully jewelled with a temperature compensation device and a ruby stone cylinder escapement. These watches were made as demonstrations of Arnold's talent and, in terms of style and substance, were similar to other "conversation pieces" being made at the same time as those being produced for James Cox and made primarily for export to the East. The technical challenge Arnold's facility and ingenuity, coupled with his undoubted charm brought him to the attention of the Astronomer Royal Nevil Maskelyne, who at this time was seeking a watchmaker skilled enough to make a copy of John Harrison's successful marine timekeeper. A full and detailed description of this watch was published by the Board of Longitude in 1767, entitled "The Principles of Mr. Harrison's Timekeeper", the intention clearly being for it to act as a blueprint for future quantity production. In fact, it was a highly complex and technically very advanced piece of micro engineering, and capable of being reproduced by less than a handful of watchmakers. However, the challenge was taken up by Larcum Kendall, who spent two years making a near identical copy (now known as "K1") that cost £450, a huge sum at the time. Although successful as a precision timekeeper, the Admiralty for obvious reasons wanted a timekeeper on every major ship, and Kendall's was too expensive and took too long to make. Kendall made a simplified version (K2) in 1771, leaving out the complicated remontoir system. But the result was still too costly and, moreover, not as accurate as the original. In retrospect therefore, it was a significant occasion when in 1767, Nevil Maskelyne presented John Arnold with a copy of the "Principles