If you download the manual - take a good look at the pictures and compare to your machine - that way you'll know if it's a Model 99 of that vintage. There will be a manual revised 1939, and that is probably the closest to your machine. Singer made some modifications over the years - Singer first came out with the manual 18139 (99-13) in 1925, and then issued revisions in 29, 33, 36, 39 and 49 - and possibly others that I've not seen yet.