Most xylophones have the tuning pitch stamped on the "A" pitched bar,
for example A=435 which is stamped into the wood. If it is not stamped
anywhere, a strobe tuner with an adjustable pitch control can be used
to determine exactly where the xylophone is in pitch. Check carefully
as it may not be precisely in tune as the octave A may be out of pitch.

With a strobe tuner it is possible to adjust each bar to be almost
perfectly in tune (scraping the back side in the arched underside).
Once you have established the pitch, say 35 cents flat, tune the piano
accordingly.  You can tune with a tuning fork, but the strobe is perfect
for setting the tuning, especially with pianos with tuned pitch
percussion instruments.

Greg Filardo