Laser distance meter: replacing the tape, or not
How does it work?
The instrument sends a pulse of light at the target and measures how long the reflection takes to come back, or the phase shift of the signal. The distance follows from that. In practice: aim, press, read. The beam needs a surface that sends back enough light: glass or a mirror send it elsewhere.
Where does the distance meter win?
On four fronts: long runs, where a ten-metre tape takes two people to unroll; heights, aimed from the floor instead of climbing a stepladder; cluttered rooms, where the beam passes over the furniture; and repeated take-offs, with areas and volumes worked out inside the instrument.
- Long runs. A ten-metre tape takes two people to unroll and twists on itself. The laser measures on its own.
- Heights. Under a ceiling you aim from the floor instead of going up a step ladder.
- Cluttered rooms. The beam passes over the furniture.
- Repeated take-offs. Areas and volumes are worked out in the instrument, with no spreadsheet.
Where does the tape stay essential?
In four cases the laser cannot: follow a curve or an outline, since it measures only in a straight line; measure inside a box or a duct, for want of a target; transfer a dimension onto a piece to be cut, where the tape doubles as a straightedge; and measure below its minimum distance, where it refuses.
- Following a curve or a contour: the laser only measures in a straight line.
- Measuring inside a box or a duct, where there is no usable target.
- Transferring a dimension onto a piece to be cut, where the tape doubles as a rule.
- Measuring a very short distance: below the instrument's minimum, it refuses.
Which settings falsify a reading?
Three, and they go unnoticed: the measuring reference, which shifts the starting point by the length of the body on every dimension; the unit, which brings in a factor of 100 or 3.28; and the active mode, which returns a result with no bearing on what you think you are measuring.
| Setting | What it changes | Typical error |
|---|---|---|
| Measuring reference | Starting point: front, back or tripod | The length of the body, on every reading |
| Unit | Metres, centimetres, feet | Factor of 100 or 3.28 |
| Active mode | Distance, area, volume, Pythagoras | A result that means nothing |
The measuring reference is the most treacherous: it shifts every dimension by the same amount, which only shows up at assembly.
What is the stated range worth?
It is measured on a well-reflecting target, in moderate light. In full sun, on a dark wall or a steeply angled surface, the real range drops markedly and the instrument may refuse to read. A target plate — a plain light card set on the point you are aiming at — often restores the reading.
How do you measure a point you cannot reach?
That is the Pythagoras function: you measure two sides of a right triangle and the instrument works out the third. It serves to take the height of a gable from the ground, or the width of an opening you cannot cross.
It assumes a genuine right angle: if the sight line is not square, the result is wrong with no warning.
And for setting out?
The distance meter measures, it does not set out. To carry a reference across a whole room you need a laser level — the criteria are in this guide. The two tools complement each other: one takes off, the other sets out. Ours state 80 and 120 metres: both models.
- The distance meter measures on its own, quickly, over long runs.
- It does not follow a curve and it needs a target.
- A measuring reference set wrong shifts every dimension.
- The stated range assumes a good target and little light.