If you have a drone, you can use this trick to figure out the size of an object captured on camera.

The angular field of view (often called FOV) is a measure of the angular size for an image produced by a camera. Different cameras have different FOV.

A new method is presented for physically measuring drivers' field of view in rearview mirrors. A portable coordinate measurement apparatus (FARO Arm) is used to measure the mirror locations, contours, ...

Measuring devices have become sensitive enough to detect the gravitational forces between tiny objects and may soon cross the quantum threshold.