In the fields of mathematics and science, the corner mark D under e usually represents a unit. Where e stands for natural logarithm and d stands for numerical value, which together represent the magnitude of quantity. For example, the corner mark -3 below 1000e indicates 1000, or11000.

In chemistry, the corner mark D below E is also widely used. For example, in the description of concentration, the corner d below e is often used to indicate the concentration of substances in solution. In addition, in the acid-base reaction, the angle D below e is also used to indicate the pH value to indicate the pH value of the solution.

In electronics, the corner mark D below E also plays an important role. It is used to describe the frequency and period of electrical signals. For example, when we adjust the channel of radio or TV, the frequency unit displayed on the panel is the corner mark D below E. At the same time, it is also widely used in digital circuits and computer science as a standard to judge the stability and signal-to-noise ratio of metering circuits.