Find out now, how to find the numeric value of the measurement. Measure the length of a piece of fabric can, putting the meter to it, how it's done in stores. In figure. 1.1 shown millimeter scale, which shows a rectangle with sides of L=12 mm and b= 10 mm. The area of a rectangle can also be measured, stacking inside it a sample of area units, for example, 1 mm3. The calculation shows, inside the rectangle that contains 120 squares with sides of 1 mm, t. e. the area of a rectangle is equal to 120 mm2.

Measurement, in which the value is determined by direct comparison with its unit, called direct measurement. The examples above are direct measurements of length and area.

However, direct measurement does not always yield sufficiently accurate results, in addition, it is not always feasible and convenient. In figure. 1.1 depicts a circle with a diameter of 7 mm. If you want to find the length L of the circle, it is more convenient to measure not the circumference, and its diameter and then calculate L by the formula L=πd, or L=2πr.

If you want to measure, the area of a circle, awkward - to calculate the number of square millimeters inside circumference. Easier and more accurate, measuring the diameter, to compute this area by the formula s=πd²/4, or s=πr². By measuring the length and width of the rectangle, its area can be calculated by the formula in=1Ь.

Measurement, in which the numerical value of the magnitude is according to the formula by calculating, is called indirect measurement. In practice (in science, and in technology) often have to perform indirect measurements.