What is the method of measuring distance with a telescope

Pick up the telescope, first adjust the interval and focal length of the eyepiece, and you will clearly see that on the glass plate of the right tube, there are cross divisions engraved. From the intersection of the cross, the left-right division is called the direction division, and the up-down division is called the high and low division. When measuring directional angles, use the directional division; when measuring vertical angles, use the high-low division. When measuring, keep the telescope level and aim any direction division (or high and low division) at one end of the target. Read the number of bits between the two ends of the target, which is the direction Angle (or high and low Angle) of the target. After measuring the direction Angle (or high and low angles), the distance can be calculated according to the following secret formula based on the known width (or height) of the target. Distance = target width (or height)×1000/ key number

The principle is: when the Angle at the center of a circle is small and the radius is large, the chord length is used instead of the arc length. Then: Radius ≈ chord length × Angle /2π≈ chord length/radian

If the unit of the Angle is changed to 2000π/360 (=17.45) times a 360-degree Angle, the new unit of the Angle is called the decimal place (1000 times the radian system to avoid decimals). When measuring distance, the distance formula is simplified, facilitating quick calculation. In fact, in Europe and America, the circumference is divided into 6,300 equal parts (not 6,282), while in Russia, it is divided into 6,000 equal parts. Some telescopes directly mark distances on scales based on a human height of 1.7 meters, a shoulder width of 0.7 meters, or the width and height of a vehicle. The distance measured by a telescope can only obtain approximate values because it is necessary to estimate a scale of the target.

Distance measurement with a rangefinder uses the triangulation method. It is not necessary to know the scale of the target. The distance between the two objective lenses of the rangefinder is taken as the length of the base of the triangle. A point on the target and the base form a triangle. By measuring the Angle, the distance from a point on the target to the objective lens can be measured by solving the triangle. As long as the base of a triangle is long enough, the Angle measurement can be very accurate. In practice, since the base length is known, the distance will definitely be directly marked on the mirror when measuring the Angle. I also want to know the specific operation method in detail. Please give me your advice if you have used it.