Antique thermometer Johann Holtzmann 1800 rare

Description

Very rare thermometer, scale in reaumur. Produced by Johann Holtzmann. The thermometer is in very good condition. Silver case, no hallmarks. Glasses on both sides are mineral spherical. Enamel dial without defects. Diameter without protruding parts 52 mm. The original wooden case is covered with leather with velvet inside. There is very little information on this manufacturer. Here's what I learned from a site that sold a similar thermometer.
Rare pocket-sized bimetallic thermometer in the shape of a pocket watch.
Diameter is 52mm.
It has scale in Réaumur, white enamel dial with opening allowing to see the mechanism. The case is made of silver.
The thermometer is based on the design of Frédéric Houriet, and it's further developed by his son-in-law Urban Jürgensen and described in his General Principles of Exact Time Measurement (1805).
There isn't much known about Johann Holtzmann.
The National museum of Scotland and Deutches Museum in Munchen are being kept two thermometers by Holtzmann.
The Scottish museum describes it as produced circa 1775, what is definatley to early.
The Deutches Museum mentions old catalogue card equally with 1775, but mentions that the watchmaker Johann Holtzmann is registered in Vienna about 1800s and producing this type of thermometers circa 1830s, what is correct as I believe.
The comparable thermometer by Holtzmann was presented by Antiquorum on the sale of 14 November of 2004 with estimate 5000-7000 CHF.
I will answer all questions.