Glossary · Regulation
Isochronism
The property of keeping the same rate regardless of amplitude or state of wind.
Explanation
Isochronism is the property of keeping the same period of oscillation regardless of the amplitude of the swing. A perfectly isochronous balance would keep the same rate whether fully wound or nearly run down. Real hairsprings are not perfectly isochronous; terminal curves such as the Breguet overcoil were developed to bring the balance closer to it, which is why chronometers and good watches use them.
In the object catalogue
Catalogued objects whose own source record mentions “Isochronism”. The quoted line shows where; it is the seller’s or museum’s wording, not independent verification.
Pocket watch
Waltham Vanguard Railroad Pocket Watch, Model 1908, 16s
“This open-face Waltham Vanguard railroad pocket watch dates to circa 1949 and is built on a 16s Model 1908 platform. Housed in a 50.8 mm 10K yellow gold-filled Keystone case, it…”
Movement
Illinois Watch Co. Grade 187 pocket watch movement no. 1569915
“This pocket watch movement was produced by the Illinois Watch Company under Grade 187, Model 4, bearing serial number 1569915 and dated to circa 1901. It is configured in the 16…”
Pocket watch
South Bend 'The Studebaker' Grade 223 Open Face Pocket Watch
“This open-face pocket watch is identified by the source as a South Bend 'The Studebaker' Grade 223, Model 2 timepiece dating to 1912. Sourced from the United States, it features…”
Pocket watch
Illinois Bunn Special Type III 60-Hour 16s pocket watch
“This open-face American railroad pocket watch is an Illinois Watch Co. Bunn Special Type III dating to 1928, according to the source. The seller reports it is powered by a size …”
Pocket watch
Elgin Railroad Grade No. 349 "Father Time" 18s Pocket Watch
“This Elgin open-face pocket watch is dated by the source to 1905 and features an 18-size, 21-jewel manual-wind movement recorded as Grade 349, also known as the Father Time. The…”
Pocket watch
E. Howard Watch Co. 16s Grade Series 3 Pocket Watch
“This antique size 16s hunter case pocket watch was manufactured by the E. Howard Watch Co. and is dated by the seller to circa 1906. The timepiece is driven by a manual-wind Mod…”