Ancient Measurements
Distance
Before standardized equipment, many measurements were based on parts of the body, such as a hand or foot—hence the American “feet.” These measurements became more accurate when standard rulers were introduced. A known, reproducible standard would then serve a specific geographic area.
Later, agreements were made to produce a standard metal bar with two marks that were very carefully produced. The distance was designed to represent a fraction of one ten-millionth of the distance from the equator to the north pole.
The bar was made from a very stable material called platinum-iridium and was stored in an area where environmental conditions like temperature were kept as constant as possible.
More recently, however, the definition of a meter was changed to be even more accurate. It was defined as the distance that light would travel in a particular, very small fraction of a second. This distance is very standard and can be reproduced anywhere.
Time
Similarly, the measurement of time has also become much more accurate over the course of history. The earliest measurements were based on the length of a day, or the amount of time between sunrise and sunset.
More accuracy was obtained with the invention of the sundial, which could divide a day into a number of parts. Special candles were built that were meant to burn at a steady rate, which provided a more accurate means of telling time.
Hourglasses, water clocks, and then pendulum clocks provided significant improvements. Much more recent clocks utilized electronic devices such as a tuning fork, a quartz crystal and then atomic clocks for vast improvements.
Weight
Weight measurements and scales have followed a very similar path. Some of the earliest examples of weight measurement were a simple rod that was suspended by a string in the middle. A pan was attached to each end and the product that needed to be placed in one pan, while stones representing a known weight were added to the other until the rod was balanced.
In fact, many of our earliest known written histories dwell on the requirement for society to use “true weights.”
The most ancient scales were rudimentary balances consisting of a lever with two pans suspended at equal distances from the fulcrum. When an item—such as a sack of gold coins—needed to be weighed, it would be placed in one of the pans. Known weights would then be added to and taken away from the opposite pan until the lever was perfectly balanced in a horizontal position. By calculating the total of the known weights, it was possible to determine the weight of the object in the other pan.
This system and similar variations were used until the late 1700s when new weighing technologies were invented. However, these inventions were not as accurate as the electronic systems that were designed and perfected in the 20th and 21st centuries.
Analog Scales
The next innovation was an analog scale called a spring scale, which relies on the concept that a force placed on a spring will stretch the spring a known distance its “spring constant” is known.
An indicator on the spring will move up and down a set distance against a gauge, which is marked with various weight measurements. When the force of the spring and the force of the object being weighed are in equilibrium, the correct weight can be read.
The most common type of spring scale is the bathroom scale, which combines the force of four levers coming from each corner of the scale to stretch a spring and spin a gauge.