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Still a common specification for movement diameters, although they are dimensioned since long in mm (millimeters).
The idea was to specify the monting diameter matching the aperture in the case. So this diameter should be a bit smaller than the specified size in lignes, and the mounting flange should be reasonabliy bigger, to prevent that the movement falls through the case.
Unfortunately many data sheet specifications are simple lies, making them useless. Big movements were specified bigger than actual, and it could happen that a movement fell through the case with the according mounting diameter. And the competition for the smallest movement made many appear substantially smaller on papers than in reality.
1''' (ligne) = 2.2558291mm
1''' (ligne) = 0.088812168" (inch)
|Size after Lancashire gauge
Mainly used by U.S. manufacturers, but all over the world manufacturers made movements matching this system.
The Lancashire gauge demonstates how a good idea, the standardization of movements, can be spoiled so far that the same movement appeared with different sizes in different catalogs. The rules to determine the size were not uniform, and moreover changed with the time.
The most common but still crazy system is as follows:
1) Base is 0 size = 1" (inch) diameter, and each step up adds 1/30".
2) 5/30" was added for the mounting flange, except sizes over 16 size, in which case 6/30" was added until about 1910.
3) After about 1910, uniformly 5/30" was added for the mounting flange.
4) Unfortunally it was not common to make the flange as wide as mentioned above, but for many movements it was applied.
5) When movements became smaller than 0 size, first notations like 00 size, 000 size, with a 0 for every step down. But this became soon awkward.
6) So the steps down got the notations 2/0 size, 3/0 size, 4/0 size etc, starting with 2/0 size (equivalent to 00 size) for the first step down.
Created by Aaron Dennison, and used by the case manufacturer Dennison
Set of mounting diameters (case apertures) optimally covering the common sizes after Lancashire gauge and in Paris lignes.
Base is the size A with an aperture of one inch diameter, and the following sizes have 1/16 inch increment.
...the alternative - free of charge!
|Dr. Roland Ranfft
|phone +49 (0)4423 9849691
|Last update: 01-22-2020|