The first weighing device was recognized in Egypt and the Babylonian era, as early as 5000 BC. This ancient scale is a simple wooden balance with a hole at each end and a hole in the middle. The rope passing through the middle hole is used to support the balance beam. The weighing pan is supported by a rope that passes through the holes at both ends of the balance beam. This structure is called an "equal arm balance", in which the weight of an object in one weighing pan is equal to the weight of an object in another weighing pan, and the center support serves as a fulcrum.

Around 2000 BC, some improvements were made to the original structure, and a vertical hole was drilled from the top of the balance to connect the horizontal holes at each end of the balance. The slings of each weighing pan are threaded from the vertical holes through the transverse holes to the weighing pan. In this way, due to the weight of the weighing pan, the sling remains in fixed contact with each end of the balance beam, and this improvement helps to more accurately determine the length of the lever arm.

This balance is the only known weapon before the Roman era. However, this does not mean that it retains its original structure. During the five thousand years, the main improvement was to greatly improve the accuracy and convenience of the balance.

In about 1000 BC, the above-mentioned scale was improved by replacing the rope pivot with a bronze ring. Although the bronze ring does not improve the accuracy of the scale, it does improve the portability and convenience, making the use of the scale more common. Then, about 500 BC, the use of hook and loop began. The fulcrum pin is secured to the shackle so that the balance beam is easily removed from the fulcrum pin. Soon after, by lowering the fulcrum from the center, the lower load can balance the heavier load and start using the multiple lever (non-equal arm balance).

For thousands of years, the equal arm balance is the only instrument used worldwide. Around 400 BC, a new weighing principle emerged, known as the "Denmark Bismarck Weighing Apparatus". It consists of a wood pole and a scale hook that holds the larger weight at one end and the scale hook for the load on the other end. The fulcrum can be moved and the rope or metal ring slides along the scale until it is balanced.

The weight is read through the series of notches on the underside of the scale. Although it is not very accurate, it is very popular around the world and uses a different name. Weighing controller
This balance was improved in 200 BC, when the Romans invented the steelyard. Unlike the Bismarck, the scale has a fixed fulcrum and is based on the principle of equal torque.

The steelyard is considered to be a reliable and accurate scale. The principle is to apply strength from a distance. The product obtained by multiplying the force by the distance is called the "torque". If the sum of the two moments is equal, the system is considered to be in equilibrium.

The scale is also the first to use the sliding weight principle. One scale hook is attached to the shorter arm for supporting the load, and the other scale hook is attached to the second pivot point for supporting or hanging the scale. The load is weighed by moving the weight along the scale. Compared to an isometric balance, the larger advantage of a steelyard is the ability to weigh a heavier load with a lighter weight. For example, the beam of an equal arm balance is a single lever with a ratio of 1:1; the scale of the scale is a multiple lever with a ratio of 5:1.

In 1490, Leonardo da Vinci, a famous painter, sculptor, architect and engineer, designed an instrument for automatic balancing and automatic indication.

He designed two scale structures using the same principle. In one configuration, the semi-circular weighing pan is suspended from the column by a rotating shaft, and the rotating shaft is located at the center of the diameter of the weighing pan. The weight hanging from one corner of the weighing pan rotates the scale, slowly increasing the weight corresponding to the load. When the two weights are balanced, the rotation stops.

The other uses a triangular structure, the triangle is suspended at its highest point, and the load is suspended at one corner of the triangular base. In this case, the load causes the triangle to pivot about its rotation in the same manner as the semicircular scale. Da Vinci's automatic indicator scale is as important as the automatic balance scale. This scale has a reader, located on the arc of the weighing pan, and the development of the three-weigher.