The recent NAWCC "Watch and Clock Bulletin" had an interesting article discussing the 1921 congressional tariff hearings (as related to the tariff's imposed on watch imports). I've known for a while now that the markings on the movements were related to these tariffs, so I started digging into it a bit more, and I've come up with the following that might be of interest to those looking to more accurately date their watches.
Prior to the tariff act of 1897, there was no real consideration of what "kind" of watch was being imported; all watches and clocks were taxed at a rate of 25% ad valorem. That changed in 1897, when they mostly switched to a flat tax that was based on the number of jewels. This ranged from $0.35 for 7 jewel and lower up to $1.25 for 17 jewel watches. Above 17 jewels, the tax was $3.00 + 25% ad valorem. The goal here was to protect the bread and butter of American production, the high-end railroad grade watches. However, there was no requirement to mark the movements, so any markings would have been at the discretion of the watch companies.
The tax rate didn't change much in 1909 or 1913, other then the addition of a 25% ad valorem to 17 jewel watches. However, starting in 1909 the tariff act required imported movements (as well as dials and cases) to include indelible markings. The 1909 act required:
Dials: had to include the country of origin
Cases: had to include the country of origin and name of manufacturer.
Movements: same as cases, but also required the number of jewels and the number of adjustments.
The 1913 act was pretty much identical to the 1909, with one exception. As of 1913, watch companies could state "unadjusted" if the watch was unadjusted.
The list of adjustments at this point was mostly just for the sake of ensuring that the quality of the watch was apparent to the consumer, I believe, because there was no difference in the tax rate.
That changed in 1922. For watches with 17 jewels or higher, the ad valorem was removed, and replaced with a tiered system of flat taxes based on the number of adjustments. These ranged from $2.75 for an unadjusted watch up to $6.50 for a watch adjusted to 5 positions. Watches with more then 17 jewels were taxed at $10.75. Most importantly (for the sake of my topic), they modified the requirements to change the "Name of Manufacturer" to "Name of Manufacturer or Purchaser". They also added text indicating that "only jewels which serve a mechanical purpose as a frictional bearing be marked as herein provided".
I wasn't able to find the actual tariff texts for beyond 1922, but another book described some of the changes of 1930, 1936 and 1955. Most notable is that watches with no more then 17 jewels were taxed a flat rate for each adjustment (with temperature counting as two adjustments), and there was a flat tax for each jewel in excess of 7.
If anyone knows of site that shows scans of the tariff acts from after 1922, let me know!