Hi Jerry,
The highlighted paragraph concerning the brand name does not give any details on the 'Sola' name specifically. It talks about the Cyrus trademark and finally lists other trademarks that were registered by Thommen. There are no dates attached to the various trademarks listed.
It reads 'was used in 1880' (regarding the Cyrus brand), this does not mean that the usage was stopped after 1880
The fact, that even the latest models of Revue-Thommens movements are called GT and that a UK-website states: "Up to 1961, about one hundred different G.T. calibres were developed and produced. From 1961 onwards, further calibres were added, and were identified by initials." gives a concluding hint that the company never really discontinued the usage of the G.T. name or logo so we can dismiss the “GT” as any indication of age.
Finally, we can date this watch to 1900-1905 (earliest date possible because of the case style), Now I think some confusion about Elinvar has crept in here we use the term loosly for anything that has a silver hairspring, as I say the Swiss where normally ahead of the USA in watchmaking and Elinvar ( I believe a trade name) is a later version/improvement of a invention of Guillaume invented the Invar steely alloy in the late 1890s, it was never in use for watches until 1912 (another indication of date). Elinvar, an improved alloy made especially for watches, came in use in the early 1920s. also the non compensated balance is being confused here with the USA Elinvar non compensated balance as we know it, this is simply a cheap monometallic steel balance and no doubt when setup correctly would give excellent timing results and reliability.

I'm pretty sure that the case is German.
The Hallmark is a German mark.

The one that looks a little like a cupcake! hehe
Sorry that's all I could think of to explain it.

Hi Sheila,
I cannot identify the large hallmark at the top and it does look like a 'cupcake'.

However, the two smaller ones on opposite sides of the 0.585 mark are squirrels, a swiss hallmark for gold.
So go figure....

Thanks for your input.

Regards,
Jerry

Jerry, Chris,

I have a Revue GT here, which has a similar balance and hairspring assembly, and the hairspring is also alloy - probably an elinvar type material.

The balance isn't steel, but a non magnetic and probably 'temperature change' resistant alloy - I also stuck it next to a huge horseshoe type magnet, and although everything not nailed to the bench got nailed, the only thing on the balance that did was the hairspring stud and staff.
(Don't worry, both the staff and hairspring are 'hors de combat' anyway)!

I wouldn't get hung up about the shape of the stud too much either, it would be a rare watchmaker that never in his or her life unintentionally modified a hairspring so it didn't work anymore - the original (if this one isn't) could simply have been nuked by accident during service or simply broke at the stud where the stud is crushed onto the spring - either case would necessitate replacement by whatever was available!

I'm with Chris on the age of the watch though, say post WW1 maybe.

Sorry I can't help with the hallmarks, realised all my books cover silver marks mainly, but the large shield appears to be a crown similar to that used in the UK, just the shape of the shield that differs.

Best regards

John

Thanks to all who have contributed to this string, I really appreciate your input.

May everyone enjoy a HAPPY NEW YEAR....

Regards,
Jerry