In the early ages of the world, when countertrade was the global method of swapping goods, people didn't actually feel the need to weigh their goods. But as soon as the mediums of exchange with a relatively fixed value were introduced, the need for finding out how much weight a product had, was crucial for defining the actual value converted into the current currency.
This is why smart people all around the world were experimenting with weights, laws of physics and fortune. The earliest scales were found in an egyptian grave. They were the pre-stage of the beam-scale, the function was the same. This find spot is dated on the 5th millennium before christ, that means that these scales are at least 7000 years old. This type of balance was relatively inaccurate and only intended for the approximate determination of weights, since the position of the weighing bowls was a strong influence on the detected weight of the goods.
This basic type of a scale was often improved by other cultures: The etruscans for example improved the weighing accuracy of these. The romans also had another type of scale, which was a beam scale with different arm lenghts and a movable weight, which was slideable along a tagged beam. In 1669 the board balance was invented by the frenchman Joachim de Rome Rosentahl. It had the advantage that the position of the weighted good didn't affect the weigh results. In 1763 the swabian pastor Phillip Matthäus Hahn built a scale with a direct weight display. Kitchen scales were invented in the first half of the 19th Century. In 1939, two american engineers experimented with electrical resistances and lead the path to the modern digital scales that we can find nowadays.
The most common forms of scales are: Digital scales, beam scales, pocket scales, industrial scales and spring balances. Every scale has its own speciality and can be used for many other purposes than the name would reveal.