Tachometer: a device used to measure the rotational speed of a spinning device [link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXPT31&P=RF]http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXPT31&P=RF[/link] For model airplanes, they're usually optical devices that can count the times a propellor blade breaks the light entering a photo sensor.
My instructor mentioned something about a thread locker. What is that?
The most popular brand is Loc-Tite. It's a chemical you place on the screw threads before screwing your parts together, and it makes it difficult to unscrew so that it'll stay tightly put together even when the engines vibrations get to it. There are several different grades, as well. The red type is quite permanent. The blue holds well, but is removable with some effort. For most situations, I use the blue.