Trying out a strap whimsically different from the black shell cordovan that comes with the watch... addendum: after some flack from friends here, it's back on the black one...
"Loaned" this one to a friend and they sent me this rather impressive snapchat. Better photo than I've ever taken of it. Much less hairy too
Egad that looks familiar...but on second thought, I'll bet yours sports a cal. 551! (mine is cal. 505)
Hah, a sibling! Yes, it is cal. 551. I wouldn't be able to guess what your is without seeing the back though. Yours is in very nice condition!