French 18 carat gold decorative buttonhole watch Circa 1900

Rose gold diamond and ruby set buttonhole watch
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An extremely rare, probably French 18 carat rose gold, diamond and ruby set buttonhole watch, circa 1900. A cylinder escapement. White enamel dial with blue Arabic numerals and a red 12, spade hands. A plain case, the bezel is alternately set with diamonds and rubies, punched “bté sgdg. H.R”.
The case is numbered.
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Diameter: 23 mm
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Diameter bezel: 11.5 mm
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Weight: 13,5 g
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Signed: No name
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The gold version of buttonhole watches, additionally set with gems is extremely rare.
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BTÉ S.G.D.G. H.R meaning
On a 1900 buttonhole watch, these letters probably are French patent markings and manufacturer initials:

• BTÉ is an abbreviation for Breveté (Patented).
• S.G.D.G. stands for Sans Garantie du Gouvernement (Patented Without Government Guarantee). 

This statement was a mandatory legal disclaimer in France under the 1844 law and remained in use until 1968. It indicated that the French government granted the patent without formally assessing the invention’s novelty, value, or technical validity, leaving the patent entirely at the applicant’s own risk. 

H.R
These letters typically represent the manufacturer’s initials or a specific trademark. In the context of early 20^th century French watchmaking and jewelry, “H.R” is often associated with the maker of the case or movement.