The whistles of a calliope are tuned to a chromatic scale, although this process is difficult and must be repeated often to maintain quality sound. Since the pitch of each note is largely affected by the temperature of the steam, accurate tuning is nearly impossible; however, the off-pitch notes (particularly in the upper register) have become something of a trademark of the steam calliope. A calliope may have anywhere from 25 to 67 whistles, but 32 is traditional for a steam calliope.