problem of the positional adjustment of balance controlled watches. This device, known as the Overcoil balance spring, is still used today in most precision mechanical watches. Another part of the patent concerned the escapement—a modification of Arnold's pivoted detent escapement that essentially mounted the detent on a spring. The specification only shows the part of this escapement that is the method of impulse on the impulse roller. Patents and plagiarism The fact that Arnold had gained great success by modifying the technology of the timekeeper by means of simple yet effective mechanical techniques also meant that other watchmakers could copy these methods and use them without permission. This is why Arnold took out his patents. Two other makers also made precision watches with the detached escapement: Josiah Emery and John Brockbank. Both were friends of Arnold, and both employed the highly skilled workman and escapement maker Thomas Earnshaw. Josiah Emery used, with Arnold's permission, an earlier form of his compensation balance and helical balance spring, in conjunction with the detached lever escapement of Thomas Mudge. John Brockbank employed Earnshaw to make his pattern of chronometer, but with Brockbank's design of compensation balance. In 1780, while making these chronometers for Brockbank, Earnshaw modified the pivoted detent by mounting the locking piece on a spring, thus dispensing with the pivots. Arnold managed to see this new idea and promptly took out the 1782 patent for his own design of spring detent, but it is not known whether this preceded Earnshaw's own idea. Therefore, there has been a great deal of debate over who invented the spring detent escapement, Arnold or Earnshaw. This argument, first initiated by Earnshaw, has been continued by horological historians (such as Rupert Gould) to present day. However, the argument is irrelevant. In recent years, research has established that Arnold's success was not due to the form of detent escapement, but to his original methods of adjusting the balance spring for positional errors by manipulating the overcoil terminal curve. For obvious reasons, Arnold tried to keep these methods secret; certainly it is recorded that he clearly expressed his concerns about possible plagiarism to Earnshaw, warning him in no uncertain terms not to use his Helical balance spring. Nevertheless, a year later, in 1783, Earnshaw—through another watchmaker, Thomas Wright—took out a patent that included Earnshaw's pattern of integral compensation balance and spring detent escapement in the multiple specification. However, both