gamma300C

My 2009 C300 has three washer nozzles with a single horizontal slot and a hole which houses a slot metal screw. The only post i found describing this set up and asking whether the adjusting screw actually changed the spray pattern morphed into a discussion of the twin slot washer and the "special" tool to adjust it. Any one have an opinion based on experience as to what my type of washer with the screw (which will move lt/rt) actually does ? A Google Search strangely does not show this set up as far as I can see.

Much Appreciated.