Use your PC as a virtual metronome
If you can't put your hands on a metronome to keep your musical tempo in check, then why not use your PC to do the job for you? It's a darned-sight cheaper than buying your own and is just as easy to use. Metronome makes a ticking sound, giving bar markers for 3/4 time, 4/4 time, and 6/8 time. To select the tempo you want to use, just click on one of the numbers, and metronome will start immediately. Click 'Stop' to stop it at any time. There's nothing more to it than that. The metronome has been designed specifically for a guitar course offered by the developer, but it should be useful for general musical needs.
Metronome is a handy tool for any musician that needs bar markers in 3/4, 4/4, or 6/8 time.