Science & Mechanics was a magazine along the lines of Popular Science, Mechanics Illustrated, and the like. I haven't been able to find out much about it other than it was in-print in the 1930s through 70s. It appears that they sold darkroom meter kits (probably among other things). I know of three: this Model 250P, the Model 102 and the A-3.

This is the earliest of the three: it appears in a Modern Photography roundup of meters from July 1963.

This one is oddly the most straightfoward meter I've seen, because it's calibrated directly in microamps, which is what pretty much all analog meters measure anyway. Microamps are a real-world value. They could have done what almost everyone else did, which is to calibrate it in "light values" of whatever scale they wanted. I don't really know what difference it would make.

So you aim the sensor at your reflected light source, use the range scale to get a good reading, then turn the meter over and use the calculator dial to calculate your exposure.

I haven't found an advertisement for it yet, but I assume this was a kit, and that the appeal of it was building it and learning something about how it worked. It certainly would have appealed to me.