http://www.singerco.com/pdf/SINGER_AG_nos.pdf According to this it is Model 15 one of 25000 and made in 1946, 7 years old than a similar one I have :D
You can download a free copy here:
http://www.singerco.com/accessories/manuals.html although it is for a treadle machine it won't really matter as it is the threading and working part of the machine which is important, is it not :P