Whether you’re checking a package on a conveyor belt, shipping packages at the post office or buying bananas at your local grocery store, scales play an essential role in our daily lives. But do you know how they work?
Scales use sensors to feel the force of gravity and translate it into a number you can read. The sensors are super sensitive and can feel tiny changes in weight, like a few grams.
Definition
The ratio of the dimensions on a model or blueprint to the corresponding dimensions on an actual figure or object. A scale is also used to represent distances on maps. A map’s scale depends on the unit system used, and many cartographers have preferred units to use for certain purposes. A scale that uses obsolete or ill-defined units will not be easily understood by modern users.
A scale that is isotropic has a point scale equal to its meridian scale and so preserves shape for small elements on the map. This is a property of conformal projections, such as the Mercator and Gall equal area projections.
A scale that is not isotropic has a point scale proportional to its latitude and thus distorts shape for small elements on the map. A scale that does not preserve shape is not an orthomorphic projection, such as the Mercator and Gall parallel and meridian equal area projections. The plots below illustrate the variation in the point scale functions of these different projections.
Units
Units of scale have been a key component of human endeavour throughout history. Confusion in determining units of measurement can lead to errors in calculations, which have serious consequences. In the past, multiple systems of units were used, but today most scientific and technological applications use a set of standardised units known as the metric system or SI. It is a coherent system based on powers of 10, with metric prefixes that act as power-of-10 multipliers to ease conversion between the different units.
For example, the unit for time is the second; the unit for length is the metre and its decimal multiples; and the unit of mass is the kilogram and its decimal multiples. Several other types of derived units are also available for expressing quantities of dimensions that cannot be directly measured, such as area or speed.
The scale of a map is the ratio between the distances represented on the map and their corresponding sizes in the real world. For example, a scale of 1:50,000 means that one unit on the map represents 150,000 cm in the ground.
Reliability
The reliability of a scale is the extent to which it is consistent and free from measurement error. A measurement instrument is considered to be reliable if it produces similar results when administered to different participants under the same conditions. For example, if you repeatedly step on a weight scale and it always reads 160 pounds, then the scale is reliable.
A measurement instrument’s internal consistency is evaluated using a statistic called Cronbach’s alpha, which measures the correlation among items that are intended to measure the same construct. Typically, the entire scale is tested for its internal consistency, and items that do not correlate well with the underlying construct are dropped at this stage.
Another aspect of a scale’s reliability is its test-retest reliability, which is determined by administering the same scale to the same participants on two separate occasions and comparing their responses. The higher the correlation between the two tests, the more reliable the scale is.
Accuracy
In the context of measurement, the accuracy of scale refers to the proximity of a set of measurement results to their true value. It is also referred to as the mean or average error, and it can be compared to the precision of a set of measurements (the degree to which they repeat themselves under identical conditions).
The term accuracy is sometimes used interchangeably with the term trueness, but these are not the same. Trueness is a statistical concept that measures the bias of a given measure of central tendency, such as the mean; it does not consider variance or standard deviation.
Accuracy can be impacted by several factors, including the quality of the measuring instrument and the human operator. In general, higher measurement accuracy implies lower error. However, this is not always the case. For example, a high level of precision can still be achieved with a low level of accuracy. This is due to the fact that accuracy depends on how close a result is to its true or accepted value.