metronome for different time signatures

I understand about tempo, but how do you set a metronome for 3/4 time or something other than 4/4. 4/4 seems to be it's default is since there are 4 beats per measure. Are there metronomes that you can set to change time in the same music piece like in Blackbird. Last question is that a metronome in the background of the song or taps on the guitar?
thx

You can just count it out in 3's instead of 4's. Unless you have a metronome that is accenting the first beat of the measure. There are metronomes that can go to whatever time signature you want, but I don't know about changing while it is playing.

If I remember, the tapping that you hear in the background was the tapping of his foot that got picked up on the mic and they decided to keep.