Lemania developed Calibre 5100 with Omega circa 1974. Omega named the movement Calibre 1045, and produced a series of Speedmaster Automatic chronographs between 1974 and 1988 that employed this calibre.
The 5100 is a particularly rugged but accurate calibre used mostly in military and space applications. The 5100 was the only calibre that met their military requirements. Among the brands who supplied Calibre 5100 military chronographs under contract were Sinn, Fortis, Hamilton, Orfina, and Tutima
SHOCK RESISTANCE: Due to its construction, Calibre 5100 was the only chronograph movement that can withstand large shocks without its chronograph seconds hand stopping. This is because its chronograph mechanism is driven directly unlike most other chronographs which use an intermediate wheel. The calibre easily withstands acceleration in excess of 7G without appreciable loss of accuracy. The calibre also maintains its accuracy over long periods without servicing. Service intervals from four to seven years have shown to be sufficient.
The dial on the 5100 has a central chronograph elapsed minutes counter that is easier to read at a glance unlike chronographs which register elapsed minutes on a subdial.
There is also 24-hour (military time) indicator at the 12 o’clock position.
Because of the central chronograph minutes hand, the 5100 dial is extremely legible, and in effect provides a large 60-minute elapsed minutes register instead of the usual 30-minute subdial elapsed minutes register. Along with the movement's exceptional shock resistance, its legibility was what made these watches particularly useful for military conditions.