Hi Laurie,I think you might have confused the calibration set up in the first step of the directions. This must be done each time the unit is powered on, placed on a different wall, or whenever it is providing ambiguous indications. For you convenience, I have pasted the operation manual below. You should download and review the entire manual - free of charge
here.1) Hold the Stud Sensor 50 flat against the surface making firm contact. 2)
Press in and hold the activation button. The greenand red LED's will light. When the red LED goes off,the unit is calibrated.
Keep holding the activation buttonduring all of the following procedures.Note: While calibrating, the Stud Sensor 50 must notbe placed directly over a stud, dense material such asmetal, or over a wet or newly painted area, or it will notproperly calibrate. If the Red LED stays lit, move toa different location and try again.2) Slide the Stud Sensor 50 slowly across the surfacein a straight line. As it detects a stud edge, the red LEDwill go on.Use the handy pencil notch located at the top of theunit to mark the stud edge.3) Repeat the above steps from the other side ofthe stud. Coming from the opposite direction, markthe other edge of the stud. The midpoint of the twomarks indicates the stud center.Cautions on OperatingThe proximity of electrical wiring or pipes to the surfaceof the wall may cause the Stud Sensor 50 to detectthem as studs. You should always use caution whennailing, cutting or drilling in walls, ceilings and floorsthat may contain these items. Always remember thatstuds or joists are normally spaced 16 inches or 24inches apart and are 1-1/2 inches in width. To avoidsurprises be aware that anything closer together or of a different width may not be a stud.I hope this helps & good luck!