A straight line graph with two variables is represented by an equation such as 𝑦 = 3𝑥 – 7. The equation shows the link between the 𝑥 and 𝑦-coordinates.

For example, on this graph, the vertical axis goes up in steps of 2 degrees. Even though 7 degrees and 9 degrees are not shown, they are still represented between the labeled points.

In this case, the line chart quickly tells us that Branch 1 shows steady growth throughout the year, while Branch 2 has some fluctuations.

Priceline.com (PCLN) in December 2012 was a different story. A trend line sat neatly across the top of the weeks ended April 13, 2012, May 4, 2012 and April 12, 2013.