LEAP-YEAR CYCLE

Leap or bissextile years have 366 days and occur every 4 years (with some exceptions, Calendar, Gregorian). Some watches display this datum.

LEPINE CALIBER
A caliber typical for pocket-watches, characterized by the seconds hand fitted in the axis of the winding-stem.

LIGNE
Line.

LINE
Ancient French measuring unit maintained in horology to indicate the diameter of a movement. A line (expressed by the symbol "') equals 2.255mm. Lines are not divided into decimals; therefore, to indicate measures inferior to the unit, fractions are used (e.g. movements of 13"'3/4 or 10"'1/2).

LUBRICATION

To reduce friction caused by the running of wheels and other parts. There are points to be lubricated with specific low-density oils such as the pivots turning inside jewels, the sliding areas between levers, and the spring inside the barrel (requiring a special grease), as well as numerous other parts of a movement.

LUG
Double Extension of the case middle by which a strap or bracelet is attached. Normally, straps and bracelets are attached with removable spring bars.

LUMINESCENT
Said of materials applied on markers, emitting the luminous energy previously absorbed as electromagnetic light rays. Tritium is no longer used and was replaced by other substances having the same emitting powers, but with virtually zero radioactivity, such as Super-Luminova and Lumibrite.