Say you need a refresher on the Pythagorean theorem. Who are you gonna call?

These men on the roof of the Y might have done the trick. They were civil engineering students who had climbed atop the YMCA building to erect a new triangulation signal, dubbed Station Northeastern.

The signal aided large-scale surveying. Triangulation divides a region into a series of triangular elements, allowing distances and directions to be accurately pinpointed by measuring a signal from two or three different points and applying a little trigonometry.

NU's signal formed one vertex in the triangle. The other two were in Mount Auburn Cemetery and the State House cupola. (In case you're wondering, the distance from Station Northeastern to the golden dome was 9,002 feet, 6.75 inches.)

These sophomores extended the triangulation network to include Parker Hill and points in the Fenway. Observations could be made simultaneously on the signal and from the station. Pretty handy for civil engineers figuring out a construction layout or a property boundary.

Of course, such profligate use of manpower is now for squares only. One surveyor with a backpackful of tools could do the same job today.

And she'd probably still help you out with that theorem.