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Understanding old crystal size measurements

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This question isn't really one of repair but more a direct question as to what the markings are on the little stickers you find on old watch and pocket watch crystals.

I understand the 1/16 measurements are lignes, the 1/4 measurements are lunettes(?), the three digit numbers are tenths of milimeters and the number typically from 1-5 is the height of a Geneva crystal, but what do the numbers measured in fractions of 1/8 signify? I did a calculation and the conversion from mystery unit to lignes is

lignes = (1/2) x mystery + 10

Any ideas?

Screen Shot 2020-07-29 at 21.20.02.png

Screen Shot 2020-07-29 at 21.20.16.png

Edited by agregate
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1 hour ago, Nucejoe said:

I have a question which I think I should ask on your here thread.

Cousins UK has various "fancy" shapes.

1 hour ago, Nucejoe said:

What if the crystal shape is elipse or some odd looking Japanese.

Based on the case reference search crystal P/N on boley.de, Cousins, or some other source. Then search Internet, mainly Ebay for NOS.

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I wrote an article about these old glass sizes once, in German however.

In short: they all depend on "ligne" = 2.256 mm.
Just multiply the figure with 2.256 mm.
Eg: "19 8/16" = 19.5 x 2.256 = 43.99 mm

Much more complicated:
Zero is 22.56 mm. 
Integers x 1.128 mm. 1/8 = 0.14 mm
Eg: "19 1/8" = 22.56 + 19 x 1.128 + 1 x 0.14 = 44.13 mm

Sizes below 22.6 mm are calculated differently (backward from 22.6!)


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