Off-square means too long, every time. The meter measures the distance the light traveled, and an angled path is longer than the perpendicular one.
The three causes, in order of likelihood
- Angle. Hold the tool square. Meters with two bubble vials in the body exist for exactly this.
- Reference edge. Most meters default to measuring from the back of the housing. Press the front against a wall with the reference set to the back and every reading is long by the length of the tool — around 10 cm (3.9 in).
- The wrong mode. A meter left in area mode returns a number that is not a distance at all.
The practical fix for angle
Take three readings, shifting your aim slightly between them, and keep the shortest. The shortest is the closest to perpendicular, because every deviation adds length.
When it reads short instead
That is a different problem. A beam clipping an obstruction — a door frame, a light fitting, the edge of a shelf — measures to the obstruction. Look at where the dot actually lands.
This does not replace the manufacturer's instructions. Every accuracy figure, measurement category, laser class and detection depth on this page is reported from the manufacturer's own documentation and named as such — none of it is calculated here. Working near a live installation, and trusting a detector before drilling, are safety matters: follow the figures printed on your own instrument and in its manual, which take precedence over anything on this site, and where a job belongs to a qualified person, hand it to one.
What gets asked here
Do the bubble vials really help?
They let you square the tool to the wall before pressing, which removes the beginner error that nobody notices. Two of the meters we compare have them built into the body.
Does surface color matter?
For whether it reads at all, yes. Dark, matt or absorbent surfaces return too little light, and glossy ones deflect the beam. A target plate solves both.
Last reviewed 31 August 2026