Of course this assumes that the piano is in tune.
Sometimes trying to tune a guitar to a piano that has not been tuned
in years can do more harm than good.
* One important thing to know about the guitar, especially
if you have played another instrument. Music for the guitar
sounds an octave lower than
where it is written. If you try and tune the guitar to the piano
thinking that they are exactly the same, you will break all
of your strings. You would be trying to tune the guitar an octave higher than where it should be.