# Understanding the Basics of Mass Measurement

Getting kids to understand the basics of mass measurement will help them effortlessly grasp the more complicated concepts in subjects like physics later on. Oftentimes people confuse mass and weight, but they are completely different measurements.

Mass deals with matter and inertia; weight is the force induced on an object by gravity.

## The International Prototype Kilogram

For more than a century, scientists around the world have defined the exact weight of an object called a kilogram. It’s a small, metal cylinder made in 1889 of platinum and iridium. It’s so important that the International Bureau of Weights and Measures, or BIPM, keeps it under lock and key. It’s known as the “International Prototype Kilogram,” or IPK. And it’s so pristine that it can only be opened by three people who release their locks at the same time.

This artifact has underpinned four of the seven existing SI base units (gram, kilogram, ampere and Kelvin) and all their derived units, such as the mole, candela, volt and hertz. But, even though it serves metrologists — scientists who study measurement science — well, its dependence on physical objects limits its future usefulness.

In 2018, delegates from 57 nations meeting at the CGPM agreed to redefine the kilogram in terms of a formula that refers to Planck’s constant, a physical property tied to electrical current and voltage. The new definition will eliminate the need for the IPK, and most national “working standards” are expected to follow suit by 2024. NIST maintains two primary prototype national standards — K20 and K4 — and a number of stainless-steel working standards that are used to calibrate them.

## The Metric System

The metric system is the universal decimal system of measurement that was developed during the French Revolution in the 1790s. Though the metric system has evolved over time, it is now the world’s most used system of measurement.

The base unit of the metric system is the gram, or g. It is joined by multiples and submultiples to create a set of units that are commonly used for measuring length, capacity, temperature, and force. The most familiar of these are the meter, kilogram, and kiloliter. Other useful metric units include the centimeter, milliliter and decimeter. Multiplication and division in metric units are done by using the number 10 and its powers, which makes conversions much easier.

The metric system is easy for people to understand and use. Its reliance on decimals means that simple calculations can be done in the head or with a calculator, and complex calculations can be easily written down. This ease of use and understanding makes it very popular around the world.

## Measurement Errors

The difference between the true value of a physical quantity and its measured value is called a measurement error. There are two types of measurement errors: random and systematic. Random error affects the precision of your measurements, how consistently values are reproduced under equivalent circumstances; it is reduced by taking multiple measurements and averaging them. Systematic error skews your measurements away from their true value in a particular direction; this type of error can be reduced by carefully calibrating equipment, and observing the results of multiple tests to detect a trend.

Errors that are caused by the instrument or environmental conditions can usually be eliminated through a thorough investigation and appropriate countermeasures like recalibrating your scale or changing the location of your experiment. Errors caused by the operator can be more difficult to eliminate, but can be lowered through careful training and reevaluation of your measurement process. If these causes of error cannot be eliminated, then a greater margin of error must be accepted.

## Measurement Accuracy

Measurement accuracy is the statistical conformity of a set of experimental data to a given normal distribution. It can be tested with a normal probability test such as the Kolmogorov-Smirnov test.

It requires that data is collected under the same conditions and over a short period of time. This includes the same instrument, same operator and, in some cases, the same day.

Achieving accurate mass measurement on a quadrupole orthogonal acceleration time-of-flight (q-oaToF) instrument is essential to a wide variety of scientific applications. The ability to measure ion masses and their distributions accurately helps scientists characterize structural characterization, early drug discovery and a wide range of other applications.

Modern mass spectrometers report accurate masses to a high level of precision. These values are reported to a few decimal places, typically up to four significant figures for masses between 100 and 999 Da. This level of precision is important to help ensure that the resulting data is free from rounding errors that may result in poor quality data.

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