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docs/reference/music/change-tempo-by.md

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+# Change Tempo By
+
+Makes the [tempo](/reference/music/tempo) (speed of a piece of music)
+faster or slower by the amount you say.
+
+## Simulator
+
+This function only works on the micro:bit and in some browsers.
+
+```sig
+music.changeTempoBy(20)
+```
+
+### Parameters
+
+* a [number](/reference/types/number) that says how much to change the bpm (beats per minute, or number of beats in a minute of the music that the micro:bit is playing).
+
+### Examples
+
+This program makes the music faster by 12 bpm.
+
+```blocks
+music.changeTempoBy(12)
+```
+
+This program makes the music _slower_ by 12 bpm.
+
+```blocks
+music.changeTempoBy(-12)
+```
+
+### See also
+
+[play tone](/reference/music/play-tone), [ring tone](/reference/music/ring-tone) 
+