It is a metronome.
A metronome
Tempo is measured in the number of beats per minute. Metronomes were traditionally used to do this, but it is more common to use music sequencers to do so now.
A device used to mark time by means of regularly recurring ticks or flashes at adjustable intervals. [Greek metron, measure + Greek nomos, rule, division.] http://www.answers.com/topic/metronome?method=26&initiator=WANS
Online metronome's and metronome applications for mobile and portable devices are widely downloadable from app stores and from websites. One notable web based metronome is webMetronome.
A metronome.
It is a metronome.
how the anemometer changed over time
The laws of physics have not changed over time. Our understanding of them has changed over time.
how has coal mining changed over time
People changed over time by growing up.
A metronome.
no they have changed over time. no they have changed over time.
how has neils bohr model changed over time
metronome.
The metronome times tempo which means speed. Look at the top of your music and you should see the tempo it is written in. Then set the metronome for that tempo. The metronome will click every time you should play a note.
well it has changed over time bye people dancing it different styles.