Here is American Watch Company Grade Model 1872 SN 871,163 in its 18K AWCo hunting case. This movement is out of the Second Run of 100 American Watch Company Grade Model 1872 movements at SN 871,101. Like the First Run of AWCo Grade Model 1872's at SN 670,001, the Second Run also features an adjustable screw or cylindrical plug bearing the curb pins of the regulator. (It may indirectly affect isochronism by changing the effective spacing between the curb pins when it is turned, but its purpose was to accommodate hairsprings of two different lengths and thicknesses.) The conventional wisdom is that this feature has to do with isochronism adjustment. The first 61 Second Run movements have 18 jewels. According to the hand transcribed Waltham factory records, the first 21 jewel Model 1872, and hence the first 21 jewel regular production Waltham watch, was SN 871,162. Therefore, movement SN 871,163 shown here is at least nominally the second Waltham 21 jewel regular production watch, preceded only by one, or perhaps two exceptional American Watch Co. Grade 20 Size Keywind movements with hole jewels on both sides of their vibrating hairspring stud arbors, but these were not "regular" products. Depending on whether the first Waltham 21 jewel Model 1872's or the first 21 jewel Grade 72 Elgin convertibles reached the market first (either way, it was darn close!), movement SN 871,163 may in fact be the second regular production 21 jewel American watch of any make, period. It is also the second AWCo Grade Model 1872 movement all of whose jewel settings are gold, as the earlier 18 jewel movements have some brass settings. The 18 jewel Model 1872 movements have five of their eighteen jewels in gold settings. The 21 jewel Model 1872 movements have seventeen of their twenty one jewels in gold settings.
Movement SN 871,163 has a square roller jewel, which is a Charles vander Woerd innovation that sometimes appears in conjunction with his patented unequal lift escapement and which sometimes, as on movement SN 871,163, appears on its own in an otherwise standard escapement. My watchmaker opines that Woerd's square roller jewel resulted in less variation than a standard D-shaped roller jewel in the depth of engagement between the tines of the fork and the roller jewel when the movement is not horizontal. As such, John argues that it at least theoretically produced smaller positional variations in rate that result from the necessary sideshake in the fork arbor and balance staff. Whether a performance improvement from square roller jewels was actually realized in practice is unknown, and Woerd himself was silent about his reasons for adopting them.
