I've owned 2. A treadle singer and a HA-1 japanese machine (my baby) i love these old straight stitch machines, they are what i learned to sew on and although ive had modern machines, i far prefer the sewing experience of vintage machines.
I've got a singer machine from 1898 the code number dates it to that year, is it worth anything i hear you say? the answer is "very little" as there are 10s of thousands of them still about to this day. Mines obviously hand wind, quite heavy and well made.
There is a knob on the front of the machine with numbers on it. Change the knob to the desired stitch. A smaller number means a smaller stitch. So, 2 would be smaller than 3.