It is possible to measure by eye using an eye gauge - a person's ability to estimate distances to objects or their sizes without the help of instruments. This feature is developed with the help of special exercises or practice, measurements can be made in several ways.
If you need to measure the distance to a moving object, then use the eye-closing tactic. Take, for example, a person walking along the opposite bank of a river.
To find out the distance to a moving pedestrian, extend your hand in the direction of the traveler's movement and focus the gaze of the right eye on the end of the index finger until the person is closed by it.
At this point, close your right eye and open your left. At the same time, the traveler would jump back.
Now count how many steps the pedestrian will take before he gets even with your finger.
Calculate the distance to the traveler walking along the opposite bank from the proportion: D / P = L / G, where D is the desired one, which needs to be calculated in steps, P is the distance that the pedestrian traveled, (let it be equal to 18 steps for example), L is the distance from the end of the outstretched arm to the eye, it is on average 60 cm, G is the distance between the pupils, it is on average 6 cm. From the formula it follows that D = P x L / G. As a result, we get: D = 18 x 60/6 = 180.
Knowing that one step is approximately 0.75 m, calculate the distance in meters: 180 x 0.75 = 135 m. The traveler traveled this distance on the opposite bank of the river.
If you need to determine the distance of non-moving objects, then use the blade of grass tactics. Take, for example, a river whose width you need to determine.
First, select two visible objects on the opposite bank of the river, which are as close to the water as possible.
Stand on the very edge of the shore, take a blade of grass in both hands and stretch your arms in front of you, while closing one eye.
Fold a blade of grass in half and start moving away from the shore until the distance between the two thrown objects is covered by a blade of grass.
Now measure the distance at which you had to move away from the beginning of the bank, and you will get the width of the river.