... .2. Mode button: angle/ slope switch ,push to change the display units,Degrees(º),Slope(%),Pitch(IN/FT).In ... time, press once the zero calibration button. The LCD displayer will display:CAL1, with sound of the buzzer ... 90°, press the button as step 1).The LCD displayer will display:CAL2, with sound of the buzzer ... 90°, press the button as step 1).The LCD displayer will display:CAL3, with sound of the ...