Looking on the net and doing a little bit of Googling I found this page that might interest someone on here. http://users.tpg.com.au/mondodec/Offcial_Omega_Museum_Calibre_ list.pdf Interesting that ST is the abbreviation for standard and SP is the abbreviation for sport, could this answer the question regarding SP found in some case backs? (See the last page) Cheers, Michael