Scales have been in use for thousands of years, some modern scales, for example the spring balance, are based on designs centuries old. Modern scales have a diverse capacity, from the laboratory scales able to weigh in micro-grammes to weighbridge scales with the ability to handle fully laden articulated trucks. There are two types of weighing scale, the analogue and the electronic or digital scale.
In the analogue scale, pressure on the weighing plate is transferred to a pointer moving over a gauge via a large spring. The size and tension of the spring dictate the weighing capacity of the scales. For the purpose of calibration a knob which may be rotated is used, this adjusts the tension of the spring slightly to give an accurate zero weight.
In the electronic or digital scale pressure on the weighing plate is converted into an electrical voltage by a pressure transducer. This electrical voltage is fed to a microchip which calculates a weight from the voltage supplied. Display electronics drive either LCD (Liquid Crystal Display) or LED (Light Emitting Diode) displays to indicate the weight of the object currently on the weighing plate.
