# How to Read a Semi-Log Graph (With Examples)

A semi-log graph is a type of graph that uses a linear scale on the x-axis and a logarithmic scale on the y-axis. We often use this type of graph when the values for the y variable have much greater variability compared to the values for the x variable.

This type of graph is particularly useful for visualizing percentage change of some variable over time.

The following examples show how to read semi-log graphs in practice.

### Example 1: Semi-Log Graph for Plant Growth

Suppose a biologist wants to create a line chart to visualize the growth of a certain plant during a 20-week period.

She first creates the following line chart using a linear scale on the y-axis: This chart is useful for visualizing the raw change in plant height from one week to the next.

However, she can use a semi-log graph to more easily visualize the percentage change in plant height from one week to the next: Notice that the y-axis is measured on a logarithmic scale.

Using this graph, we can see that the percentage growth of the plant is quickest in the early weeks and then slows down dramatically in the later weeks.

### Example 2: Semi-Log Graph for Investment Growth

Suppose an investor wants to create a line chart to visualize the growth of a certain investment during a 30-year period.

He first creates the following line chart using a linear scale on the y-axis: This chart is useful for visualizing the raw change in the investment value from one year to the next.

However, he can use a semi-log graph to more easily visualize the percentage change in the investment value from one year to the next: Notice that the y-axis is measured on a logarithmic scale.

Using this graph, we can see that the percentage growth of the investment is actually consistent from one year to the next.