Science/Engineering/Technical forums

As usual, if you've got any great ones, post them after this and eventually we might roll them all together.
Here's one to start.
Microwaves 101

The cool Shure reactance slide rule. This is also elsewhere on the board, but hard to find. It's truly worth making yourself one of these if you're playing with any kind of RF or audio filter or antenna tuner. Saves tons of time: viewtopic.php?f=7&t=213

Since I'm right now playing with "fusor with RF in there", this is coming back into use and relevance.