There are couple things you'll want to check. If it's in one of the 3 GUITAR MODEs, make sure it's in guitar mode and not guitar mode flat or double flat. Alternately, try CHROMATIC MODE.It's also possible to select something other then 440 on this unit. Press the STREAM/CENT and the MODE buttons at the same time. To increase in 1 Hz steps press the MODE button, to decrease press the STREAM/CENT button. The display will show 8/9/0/1/2/3/4/5/6/7 to indicate reference from 438-447.