Tone function

I was playing with the tone function using an example, this is on an UNO, and have found the sound and actual waveform don't seem to correlate with the frequency entered into the the function. I will investigate further but my first look seems it doesn't work as advertised. Does any one have further information on this functions frequency accuracy?

The output is not a sine, but a square wave.
The (base) frequency of the square wave should be accurate. You could try the toneAC library, which uses its own code and compare that to the default tone(). They should both be accurate.

The tone is created by a Timer, and that uses the 16MHz as clock input. That clock is divided by a certain amount, so there might be a little inaccuracy.