Hi Madi,
On the definition of Calibre, here you go from Wikipedia:
[b]Caliber: at the beginning the denomination indicated only the size of a watch movement.
Today, caliber designs a precise movement type, indicating the size, the style (men/ladies’ – mechanical / automatic/ Quartz - number of hands – calendars – complications), followed by the mark of the Ebauches manufacturer (e.g. see [1] ), duly registered with the Swiss Federal Trademark Office as well as by the Federation of the Swiss Watch Industry FH.
Each single Swiss Made movement must be marked with the caliber indication.
Following WTO’s rules applicable for Custom’s & Excise, the precise caliber must be indicated on each export invoice with the coordinated international Custom’s code.
Proper markings and calibre indication has become all the more important with the increased counterfeiting of “bona fide” Swiss Watch Brands.[/b]
By the 500121 do u mean this fellow over here ? If so, your husband is a lucky man ! I believe the specifications are per the official writeup found here.
500121 would be in red gold, and has a black dial, and is boutique exclusive and is a limited edition..
500106 however is in white gold, and has an ardoise dial, and is not boutique exclusive nor a limited edition.
500121:


500106:
