What is a unit? Why are units important when expressing a measured quantity?

Understanding standard units is like having a common language for measurement. These are widely accepted and uniform 'definitions' used across the globe to make consistent and reliable measurements.
For example, in the International System of Units (SI), a meter is a standard unit of length defined as the distance light travels in vacuum in 1/299,792,458 of a second. With standard units, no matter where you are, a meter will always be a meter, ensuring that measurements are not only consistent but reproducible as well.
By agreeing on a set of standard units, such as the kilogram for mass, the second for time, and the ampere for electric current, we can communicate and compare measurements everywhere without confusion or the need for conversion. This universal agreement is essential in science, technology, and daily life.

Why do we stress so much on the importance of units? Simply put, if we did not use units, there would be no way to understand what a 'ten' or a 'hundred' of something really meant. Units give meaning to numeric values, describing how heavy, long, or hot something is in a way that everyone can understand.
In fields like engineering, medicine, and construction, precise measurements are the backbone of safety and effectiveness. For instance, consider dosing medication – the difference between milligrams and grams can be the difference between a cure and an overdose. Units are the building blocks of the rules and regulations that protect us, make commerce fair, and ensure that we can share and compare data and results no matter where we are or which system we grew up with.

Delving into the realm of physical quantities, these are the attributes of the natural world that we can measure. Some examples of physical quantities are length, mass, time, and temperature. They become meaningful when assigned a value and a unit.
Take the speed of a car, which is a physical quantity that combines distance covered with the time taken to cover that distance. We measure it in units such as miles per hour or meters per second. This way of quantifying attributes of objects or phenomena is at the heart of all scientific and engineering endeavors, ensuring that we can accurately describe and analyze the world around us.

The process of measurement comparison is fundamental to advancing knowledge and technology. It allows us to evaluate how two or more physical quantities relate to one another.
Imagine setting up a race between two cars. We can use time as a unit to measure which one is faster. Without the comparison of time taken to complete the race (where seconds and minutes are the units), we wouldn't be able to determine a winner. In cooking, measurement comparison tells us if we need more salt or sugar, helping us adjust recipes to taste. From lab research to construction and beyond, the ability to compare measurements accurately ensures consistent outcomes and progress.