OK WE ARE OFTEN FACED WITH CONFUSING AND INCORRECT CALIBER NUMBERS QUOTED ON EBAY, AND BY OWNERS TRYING TO OBTAIN PARTS.
SMITHS REFINED THE CALIBER DESIGNATION WHEN THEY PRINTED PARTS SHEETS FOR REPAIRERS.
THE FIRST MOVEMENTS WERE DEFINED AND PROMOTED AS 12.15, THAT IS 12 LIGNE 15 JEWEL.
SUBSEQUENTLY THEY CALLED ALL THE THEN PRODUCED 12 LIGNE MOVEMENTS CALIBER 27 FOR THE SIZE ACROSS THE MOVEMENT MAIN BODY OF 27MM. THUS THE CENTRE SECONDS WAS 27 CS FOR CENTRE SECONDS. WITH I AM SURE APOLOGIES TO PATEK PHILIPPE IF THEY WERE FIRST.
THE LATER FULL DEFINITION OF BASE CALIBERS WERE AS FOLLOWS
100 11 3/4 LIGNE
200 5 1/4 LIGNE BAGUETTE
300 8 3/4 LIGNE
400 12 LIGNE
600 19 LIGNE STOPWATCH( POCKET WATCH NO LONGER PRODUCED)
THE CONFUSION STARTS WITH THE FACT THAT THE BASE CALIBER IS FURTHER ENHANCED.
E.G THE WATCH MARKED 60464 IS 17 JEWEL PLAIN BALANCE(NO SCREWS) CENTRE SECONDS
E.G THE WATCH MARKED 0434 UNDER THE DIAL IS 17 JEWEL SHOCKPROOF BREGUET BALANCE CENTRE SECONDS
PREFIX LETTERS GIVE APPROXIMATELY THE PERIOD OF MANUFACTURE
SUFFIX LETTER E IS FOR EPSILON AS WE KNOW THE GILT FINISH AT THAT TIME
OTHER SUFFIX LETTERS EXIST AROUND 1955 L M P THE LATTER TWO AS I RECALL HAVE THE SPECIAL SHOCK SYSTEM.