Swiss Regina WW1 Era Trench Watch Help

To ask what something is “worth”, assumes there is such a thing as a “market value” for a particular item. A liter or gallon of gas has a “market value”, because a lot of gas is sold in a particular market. The value for your Regina could be either your assessment of value as the owner, or the assessment of the value ascribed by someone who might buy it. But let me say that a 7 jewel, standard grade Regina watch in a silver case offered for sale would not likely attract a lot of attention. Regina watches were the little sister to Omega, and not highly sought after. Rare? I know of no reference that would list how many were made. But easily tens of thousands, to hundreds of thousands. So not rare. In short, since you are the most recent purchaser of a watch like this, it is worth what you paid in your market. Put it on eBay with no reserve, and you’ll find out what the market says it is worth!

Cool Regina trench. I also have one, with Canadian provenance; likely went overseas with a member of the Canadian Expeditionary Force in WWI. I also found a bit of information on Wiki, of all places. These are more than likely converted pocket watches (possibly smaller models meant for women?).
A few pics (not technically great!) and the info for you:

https://en.wikipedia.org/wiki/Regina_pocket_watches

Regina pocket watches
Regina pocket watches were a brand of pocket watches made by Omega that were popular in the early 1900s. The name Regina Pocket Watch was originally trademarked by LOUIS MAIER in Bienne Switzerland in 1888. The name was then trademarked by Omega in 1911, indicating that they bought the company at that time. The faces and mechanisms were imported into New York and assembled with cases in Ontario, for sale mostly in Canada.

Individually stamped production runs were made for a small fee. The result is that many Regina watches have the name and town of a vendor on their face. One watch has been traced to the Arcola Jewelry store in Arcola Saskatchewan. Regina watches are occasionally stamped with the name of an American city, indicating that some were sold in the United States.

The National Association of Watch and Clock Collectors describes Regina watches as an inferior brand of Omega, but mentions that some were adjusted highly enough to be used as railroad timepieces, which was the standard for quality watches.[2][3] The use of Regina watches for railroad timekeeping is documented on other sites as well. For example: "Some of these Regina-signed watches were Adjusted Highly Enough as to be suitable for use in railroad time service." [4]

The term 'farmer watch'[5] is sometimes applied to them. This may be because of their robust quality, the fact that they were sold in rural stores or that Canada had a largely rural population.

Some early watches, made before the Omega takeover have a date stamped on the mechanism. The company changed hands in the 1970s and the new owners destroyed many of the old records, making it difficult to precisely date most Regina watches. The records that still exist make it possible to roughly date them by their serial numbers. This list comes from an Omega memo:

From: Departement: Controle Central de Fabrication Bienne la 16 Fevrier 1970 Concerne Annees de fabrication [6]

• 1,000,000 = 1907-1910-1912
• 2,000,000 = 1904 - 1916
• 3,000,000 = 1906 - 1919
• 4,000,000 = 1910 - 1919
• 5,000,000 = 1916 - 1927
• 6,000,000 = 1923 - 1927
• 7,000,000 = 1920 - 1935

It seems that large batches of certain numbered watches were made and sold over a period of years.

The systems used for sizing pocket watches have changed over time.[7] In North America, pocket watches are usually sized by the Lancashire gauge which is based on the Size 0s being 1 inch across and increasing sizes being measured in 1/30th of an inch. The measurement is according to the width of the plate under the face, not the exterior of the case. For any important purpose the size should be determined correctly. These references contain detailed information about sizes. [8][9][10]

For home collectors, a close estimate can be made by measuring the actual face. These are common Regina watch sizes and approximate face diameters in millimeters.

18s Common 44.9 mm 16s Common 43.2 mm 13s Common 40.64 mm 12s Common 39.8 mm

Patria with protective grill

This was discussed elsewhere on the forum, but for this discussion here is my Regina (Omega) 24hr dial 21j adjusted pocket watch. Serial dates it to c1916-20. Cased in a 14k white gold-filled Illinois Watch Case Co Elgin “Tivoli” case c1924. So maybe it’s been recased, or maybe it sat unsold for a while. The confusing history of the casemaker is available here https://mb.nawcc.org/wiki/Illinois-Watch-Case-Co#Illinois-Watch-Case-Co--A-Brief-History (with thanks to @Canuck for the lead)

A typical “Canadian dial”, here it is shown during a typical Canadian summer