I thought I'd seen most all of the "household" types of Singer machines.. here's one I've never seen.
http://www.ebay.com/itm/ws/eBayISAPI...sPageName=ADME:B:WNA:US:1123
Model 24-80. Only 5,500 model 24's were produced in 1921. I do not know how many were -80's.
Serial number G9043339 dates this machine to October 11, 1921.
Interesting.