I have found that sometimes it can be difficult to tell the difference just by the serifs. The earlier watches (.013, .026) have a lighter print without serifs (usually) Later watches (.036) the numbers have heavier printing with small serifs. The 0s and 3s are always different between service and original.
Look at whether the 50 and 55 are parallel, distance between the 5s or the 5 and 0 are the same at the top and bottom or if they are slightly askew to follow the radius of the bezel.
Just perusing "flightmaster only" book, a great resource, and was looking at the author's production figure estimates. of the total 35,000 watches they estimate 14k for .013, 10k+ for .026, and 10k+ for .036. As an admittedly non precise exercise I checked sales on Ebay of flightmasters. There are 40 currently posted of which only 7 are .013, 13 are .026 and the rest .036. Roughly the same breakdown can be found in completed listings. It just seemed curious to me that with the book's assumption that more .013 references were made than the others you'd certainly think they would be more common on the sales sites. Chrono24 shows roughly the same ratios. Thoughts, rants, (no expletives please) welcome.
Interesting article, please let me add the best color photo showing the Soviet-Russian crew in their Sokol spacesuit, wearing flightmaster BTW no flightmaster watches were worn during the actual ASTP mission as none are visible on NASA TV-footage nor on NASA photos ! Only possibility remains a flightmaster taken into a PKK - Personal Preference Kit, but with a total of 11 Speedmasters flown on ASTP, unlikely... . Soyuz 19 crew in Sokol suits for the Apollo-Soyuz Test Project pose in a Soyuz mockup during preflight training...
