Dorky Poll: Favorite Tool

In the comments to the post where I noted how many more people had least favorite textbooks than favorite ones, dr. dave writes:

Textbooks… particularly SCIENCE textbooks, are not really written to be ENJOYED by anyone. They tend to be purely utilitarian. Asking for someone’s favorite textbook is kind of like asking someone to choose their favorite screwdriver.

To which my reaction is: “What’s wrong with having a favorite screwdriver?”

So here’s a new dorky poll. We’ll broaden the category a little, so as to be more inclusive, but inspired by dr. dave:

What’s your most essential tool?

I’m looking for low-tech stuff here– hand tools and the like, not “The CLAS photon tagging system” or something like that. For humanities types and those on the theory side, pencils and software packages are also elegible.

So, what’s the one tool you really can’t do without?

Like many optics types, I think I’d have to go with the 3/16″ ball driver, which is what’s used to tighten most of the screws on the optical table (the remainder are mostly 5/64″). Pretty much any optic that’s in a mount is held in place with a screw that requires a 3/16″ ball driver.

I have three of these in the lab (one on each optical table), and I still spend an inordinate amount of time looking for them when I’m working. I don’t think I could function without them.

So, what’s your favorite tool?