It appears to be an exposure device/timing for enlarging. Ilford and others made similar things without the timing feature and remote probe.
The gadget requires you to make a good print to determine the sensitivity. Take a reference reading from highlight/shadow area(can't remember). Then when you put another neg in place, you meter the same sort of area and the time is apparently determined by your test print, so with this thing push the button and you're off to the races.
The switch on the upper light turns the lamp on to compose/focus and s/l is a mystery to me. Thimking about it. S may be used to determine the sensitivity and L the aperture?
A motorcyclist is the only one who understands why a dog rides with it's head out the window.
"I had an idea once, it died of loneliness"--George
“Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”
Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2
I guess it is for automatically enlarging many prints from different negatives.
Looks like you would put the sensor near the easel pointing at the middle of the sheet of paper as it gets exposed.
With no way to set the time it probably makes an average gray print of everything, automatically adjusting for over/underexposed negs, changes in aperture and enlarger height. But always gray and never telling you how much time it used.