M

• Main plate

  Base plate on which all the other parts of a watch movement are mounted.

• Mainspring

  The driving spring of a watch or clock, contained in the barrel.

• Marine Chronometer

  Highly accurate mechanical or electronic timekeeper enclosed in a box, used for determining longitude on board ship.  Marin chronometers with mechanical movements are mounted on gimbals so that they remain in the horizontal position necessary for their precision.

• Measurement conversion

  A feature, usually consisting of a graduated scale on the watch bezel, that lets the wearer translate one type of measurement into another; such as miles into kilometres.

• Mechanical Movement

  A movement powered by a mainspring, working in conjunction with a balance wheel.

• Mineral glass

  Hardened watch glass (or crystal) that is scratch resistant. 

• Minute repeater

  A complication on a watch that can strike the time in hours, quarters or seconds by means of a push piece.

• Moon phase

  An indicator that keeps track of the phases of the moon.  A regular rotation of the moon is once around the earth every 29 days, 12 hours and 44 minutes. Once set, the moon phase indicator accurately displays the phase of the moon. 

• Moon/ sun indicator

  A wheel on a watch partially visible through a cut-out window indicating a sun and moon on a 24-hour basis. 

• Mother of pearl

  Iridescent, milky interior shell of the fresh water mollusk that is sliced thin and used on watch dials.  While most have a milky white lustre, mother-of-pearl also comes in other colours such as silvery grey, grey-blue, pink or salmon. 

• Movement

  The inner mechanism of a watch that keeps time and its indicators accurate. Sometimes called caliber or modular.