Certificate for chronometer timing or rating.

In strictly horological terms, "rating" a chronometer means that prior to the instrument entering service, the average rate of gaining or losing per day is observed and recorded on a rating certificate which accompanies the instrument. This daily rate is used in the field to correct the time indicated by the instrument to get an accurate time reading.

Already in the 18th century watches were tested in observatories for their accuracy. Observatories were independent institutions and had very accurate precision pendulum clocks. Regular chronometer certifications took place after 1850. The watches were tested for 44 or 45 days in 5 positions and at several temperatures. This service was included in the advertising of watch manufacturers.

This pre-printed certificate for timing of the chronometer of Simon Willard Jr.’s includes handwritten name of chronometer brand or maker, its serial number (#830), date of the assessment (Jun 25, 1840), recommended timing adjustments, and signature of Simon Willard Jr. with preprinted instructions under. Document is framed in a wooden golden frame.

Ht. 8.1/4” 1802.71

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