This is how you measure a height you cannot reach without a ladder. It is also the mode most likely to hand you a confident number that is completely wrong, so it is worth understanding what it is doing.
You want the height of something. You cannot put the laser at the top of it and you cannot put a tape there either. So instead you stand back and measure two distances that you can take, and let trigonometry give you the third side you cannot.
In the simplest version, you shoot the top of the wall and then the bottom of the wall from the same spot on the ground. The tool knows both slope distances, and on units with an inclinometer it also knows the angle of each shot. From that it solves the vertical height between the two points.
Two things follow immediately. The tool must not move between the readings, because the whole calculation assumes both were taken from the same point. And on units without an angle sensor, one of your two readings has to be genuinely horizontal, because the maths relies on knowing one side is at ninety degrees.
If your tool has an inclinometer, it measures the angle for you and the readings can both be at any angle. If it does not, the mode requires you to take one leg perfectly level by hand, and any error there propagates straight into the answer. Units without a tilt sensor are much harder to use accurately in this mode.
The failure mode that catches people is that the tool always produces an answer. It has no way of knowing your two readings were taken from different positions, or that you hit a light fitting rather than the ceiling, or that your tilt sensor has drifted. It does the arithmetic on whatever it was given and displays a confident number.
Moving between readings. Shifting your feet or lowering your arms between the two shots breaks the fixed origin the calculation depends on. This is the single most common source of nonsense results.
Extreme angles. Very steep or very shallow shots make the answer highly sensitive to small angular errors. If the number looks wrong, step back further and try again before assuming the tool is faulty.
A drifted tilt sensor. This one is nasty because distance readings stay perfect while every indirect calculation is quietly wrong. Bosch quotes levelling accuracy of plus or minus 0.2 degrees on Blaze units with an inclinometer. If your angle readings disagree with a spirit level by more than that, run the tilt calibration routine.
Hitting the wrong thing. Shooting the top of a wall usually means shooting whatever sits at the top of the wall. Guttering, a light, a pipe or a sloped soffit will all return a reading and none of them is the point you meant.
Before trusting an indirect measurement on anything that matters, calibrate your own judgement on something you can verify. Measure a ceiling height indirectly, then measure it directly with the same tool. If the two agree, your technique is sound and you can trust the mode outdoors where you cannot check.
Do this once when the tool is new and again if you ever drop it. It takes a minute and it is the difference between a mode you rely on and a mode you guess with.
Ceiling height over a stairwell, where there is no floor beneath you to stand a tape on. Roof edge and gutter height from ground level, which is the alternative to putting a ladder up. The height of a tree, a pole or a building for a quote. Widths across obstacles you cannot walk through, like a pond or a road.
It is worth ten minutes of practice before you need it, because the first time you use it is usually the time it matters. The rest of the modes and the technique behind them are covered in the main guide.
Everything on LaserMeasure is built the same way, from owner reports rather than spec sheets. The front page is the summary.