Find the height of a tree, pole or building by sighting through your phone camera, with or without a tape measure, using a surveyor clinometer method.
Measuring the height of something tall without climbing it is a problem trigonometry solved centuries ago. If you know the horizontal distance to an object and the angle you must look up to see its top, the height falls straight out of the tangent of that angle. This is how the height of trees, towers and mountains was measured long before lasers existed, and it is exactly what a surveyor clinometer does. The phone supplies the angle. Because the accelerometer knows which way is down, it can state precisely the elevation of the rear camera line of sight above the horizon. Using the camera axis rather than the edge of the device is what makes it possible to show the scene on screen with a crosshair: you see what you are aiming at instead of squinting along an edge. The tool uses the difference between two sightings, one to the top and one to the base, rather than adding your eye height to the result. That has two advantages. It does not need to know how tall you are, and it stays correct when the base of the object is above you, such as a window on a building or a sign on a slope, where the angle to the base is positive and the subtraction handles it on its own. The margin of error shown next to the result is not decoration. Tangent sensitivity grows quickly with distance: a one degree aiming error on a pole five metres away costs a few centimetres, but the same degree on a building sixty metres away costs more than a metre. That is why the number is shown with its uncertainty, so it is not read as if it came off a tape measure.
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It depends far more on distance than on the sensor. With a steady sight, aiming error is around one degree, which translates into a few centimetres for nearby objects and more than a metre for a building tens of metres away. The tool computes and displays that margin for every measurement, instead of showing two decimal places and pretending they are trustworthy.
Tap to turn on the accelerometer. Everything is measured on your device and nothing is sent over the internet.
Measure or pace out the distance to the base of the object, enter it, then sight the base and the top. This is the more accurate method.
Point the crosshair at the base of the object and tap Sight the base.
The computation runs entirely in the browser. The camera image is only a sight, shown live on screen, and is never recorded, saved or uploaded anywhere.