PS-150 needle selector was invented to work with bulky Singer/Silver Reed/Studio knitting machines capable of only manual stitch manipulations.
Basically, it works like a punchcard-reading mechanism but not quite automatically.
A special ruler is inserted into the slot, in which one row of the punchcard pattern is visible. The pins on the ruler are pushed in and this pre-determined combination of ruler combs is then used to manually select needles on the machine.
PS-150 needle selector typically comes with special punchcards.
The images we scanned from the official Singer Brochure.