It looks like there might be a knob missing on the arm, possibly for more decorative stitches. It looks similar to Deluxe Zig Zag #69 that the manual says is model 144 at
http://www.sewusa.com/Sewing_Machine...g_Machines.htm
What, if any, are the JA or JC numbers on the bottom?
Janey - Neat people never make the exciting discoveries I do.