When we look at data, we often use charts to help us understand trends and changes over time. Two common types of charts are linear (or regular) charts and logarithmic charts. While both serve the purpose of visualizing data, they do it in different ways that can lead to different interpretations.

What Are Linear (or regular) Charts?

Screenshot of an instrument plotted on a linear (or regular) chart.

Linear (or regular) charts are the most straightforward type of chart. In these charts, the vertical axis (the Y-axis) is marked with equal distances that represent equal changes in value. For example, if you move up one notch on the chart, it could mean an increase of 10 units, whether you’re going from 100 to 110 or from 200 to 210. This makes linear charts easy to understand for most people because they reflect values in a direct way. However, they can be misleading when the data varies widely. For instance, if you are comparing a small number like 1 with a much larger number like 1,000,000, the linear chart may make it difficult to see important trends or changes. The large gap between these numbers can obscure smaller but significant shifts in the lower range.

What Are Logarithmic Charts?

Screenshot of the same instrument plotted on a logarithmic chart for the same period.

Logarithmic charts use a different approach that helps address the limitations of linear charts. In these charts, equal distances on the Y-axis represent proportional changes rather than absolute changes. This means that moving from 10 to 100 (a tenfold increase) looks the same as moving from 100 to 1,000. This type of chart is particularly useful for displaying data that grows or shrinks rapidly—like stock prices or populations—because it allows us to see percentage changes more clearly. So even if numbers get very large or very small, we can still understand how much they are changing relative to each other.

Why Use Logarithmic Charts?

Using logarithmic charts can significantly enhance our visual comprehension and decision-making based on data. For example, if you’re tracking the growth of a company’s revenue over several years and it has skyrocketed from thousands to millions, a logarithmic chart will illustrate this growth more clearly than a linear chart would. The logarithmic scale helps highlight important trends and patterns that might be missed otherwise, making it easier to grasp how quickly something is changing relative to its previous values. In short, while linear charts are great for simple comparisons, logarithmic charts are invaluable when dealing with data that varies greatly in size or grows exponentially. By understanding when to use each type of chart, we can improve our ability to interpret information and make informed decisions based on it.