If you can't put your hands on a Metronome to keep your musical tempo in check, then why not use your Mac to do the job for you?
It's a darn sight cheaper than buying your own and is just as easy to use. Metronome makes a ticking sound which gives 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.