Coin Operated Group

90s? Serve Serve Machine, off eBay. Inside, down the middle, between the 2 columns where the stock goes, is a pair of columns, lettered A going down to Y. Each one has a tiny marker left and right which can be adjusted up or down. Any idea what these are? This machine is purely mechanical, not power...

I have came into an old Selfserve vending machine, which I would like to see if it's working etc.

Does anyone have a (PDF) manual for one of these? And anywhere I can get supplies to test it without needing to get excessive quantities of?