Correcting pitch or tape speed issues - Tip

I’m fairly new here, so this may have already been covered.
I have cassette tapes that I record into Audacity. Sometimes an old boombox recording will come out a little slow, possibly due to weak batteries when the recording was made years ago. In order to get the song to the correct pitch, I have my acoustic guitar with me at the computer. I have it tuned perfectly with my guitar tuner. Then I play the song which is now in Audacity. I compare the tuned guitar to the song and adjust the speed or pitch to match. Once I find what key the song is in, I play single notes of the melody and I can tell if I’m high or low in pitch. I have a good ear.
I hope that helps someone.