 The guitar tech also might perform any of a variety of maintenance tasks, such as checking that the string height of the guitars is set properly, modifying ("dressing") the height and arc of the frets, adjusting the intonation of the instruments, checking that tubes (valves) on tube amplifiers are working properly, and that cables are in good condition and free from crackles and hum caused by nicks and abrasions in the shielding or cable insulation.Techs also check the batteries on "outboard" devices — effects boxes, tuners, and pre-amps — and wireless transmitters, and change them as necessary.Depending on the size of a band's road crew, the guitar tech may either do this maintenance him- or herself, or, in a large touring act, delegate tasks to more-junior personnel.