# What Is a Scale?

Scale is a ratio that allows you to represent real-world objects in their corresponding size on paper. It’s used in maps and blueprints, for example.

Using scales is an important skill for anyone interested in measuring or analyzing data. However, working with scales can be confusing for people who are new to them.

## Weight Measurement

Scales measure weight in many different ways, but the basic underlying principle is nearly always the same. Whether the scale is hydraulic or pneumatic, it uses a system that reads the force of a load by measuring its displacement. Most scales also have a display that shows you the measurement. The number of digits displayed is called the “readability.”

Traditionally, mechanical balance-beam scales intrinsically measured mass (force due to gravity), while modern electronic scales use a variety of operational principles and mechanical components. However, the component that actually measures force is a digital load cell, which converts mechanical energy — the smooshing or stretching of a load — into an electrical effect.

To ensure consistency and accuracy in weighing, scales must be regularly calibrated. Scales used for commerce are often required to be NTEP approved, which means they must be tested and verified to meet specific calibration standards. When a scale is re-calibrated, the weights used to test it should match the allowable tolerances established for that particular scale.

## Measuring Force

In addition to determining an object’s weight, scales can also report its force, which is a measure of the tension of constraint on an object. For this reason, scales are sometimes referred to as force gauges or strain meters.

Most commercial and household scales determine mass by comparing an unknown with a standard reference mass. In contrast, a balance is intrinsically designed to measure mass by directly comparing the acceleration of an unknown with that of a known sample at a given location. This distinction is important because gravity’s acceleration varies by latitude and elevation.

A traditional mechanical balance-beam scale, for example, measures mass by suspending two plates at equal distances from a central point of support or fulcrum. An unknown mass is placed in one plate and standard masses, called weights, are added to the other until mechanical equilibrium is reached. A modern digital scale may use a different mechanism, such as a strain-gauge cell, to calculate weight.

## Reliability

The reliability of scales is important for the trustworthiness and credibility of research findings. A scale is reliable if its scores are consistent and stable over time. It is valid if it measures the underlying construct accurately. In order to establish both, researchers should carefully plan their experimental design. This includes conducting pre-tests to ensure that their scale is both reliable and valid.

A common measure of internal consistency is Cronbach’s alpha, which examines the degree to which the items on a scale correlate with one another. However, it is increasingly being replaced by more sophisticated measures of item-level correlation and covariance, such as Raykov’s rho or Revelle’s beta.

A criterion validity study compares the scale’s scores to an external benchmark to assess predictive or concurrent validity. This type of study is especially useful for assessing measurement error and response bias (e.g., social desirability). Criterion validity also involves examining the degree to which a scale’s items address all dimensions of the construct being measured.