I just wanted to update this ans say this one page is incredibly useful if you are building bookcases and stuff:
It helps you calculate the maximum span without sagging for different materials.
It's certainly useful. Like many others, I keep an old PC in my workshop. That gives me fast access to a lot of stuff that used to require reference books. Also, I can enlarge wording that's on the screen, if need be, which saves the annoyance of fiddling around changing spectacles.