The working principle of mechanical scales is based on Newton's mechanical laws, usually using the spring weighing principle.

Balance principle: Under normal working conditions of a mechanical scale, the platform is in a balanced state, that is, the gravity of the object is equal to the reaction force on the scale, so that the scale pointer indicates the zero scale position.

Object placement: When the weight of an object needs to be measured, the user places the object on the platform of the mechanical scale.

Spring force: The gravity of the placed object causes the spring of the scale (called the weighing spring) to be compressed or stretched. The elasticity of a spring causes it to produce a reaction force proportional to the force exerted on it.

Indicator movement: The force of the spring causes the indicator (usually a pointer) connected to the spring to move. The position of the indicator is proportional to the weight of the object.

Reading weight: The user can determine the weight of an object by reading the scale value indicated by the indicator. Scale values are usually displayed on the dial in weight units such as kilograms or pounds.

When an object is placed on the platform of a mechanical scale, the amount of compression or tension experienced by the spring is proportional to the weight of the object. The elasticity of this spring causes the indicator to move into position to reflect the weight of the object.

The accuracy of a mechanical scale is affected by several factors:

Stiffness of the spring: The stiffer the spring, the smaller the displacement it produces when subjected to the same compression or tension force, so the higher the accuracy of weighing.

Accuracy of the dial: The denser the markings on the dial, the more accurately the user will be able to read the weight of an object.

Scale stability: The stability of the scale is crucial to the accuracy of the weighing results. If the scale itself is unstable or the platform is uneven, it can cause inaccurate readings.

Environmental factors: Temperature changes and humidity may affect the elastic properties of the spring and thus the accuracy of the weighing. Therefore, in some applications, periodic calibration of mechanical scales may be required.

Although mechanical scales provide adequate accuracy in many situations, they are generally less accurate than digital scales. Mechanical scales measure the weight of an object by using the elastic properties of a spring to convert the object's gravity into mechanical motion. Digital scales use sensors and microprocessors to provide more accurate readings, while mechanical scales are better suited for applications where weighing accuracy is less important.