It's useful when you have continuous data (e.g., height, weight, temperature, and stock prices) and want to make comparisons ...

Stock charts are usually expressed as line charts ... Triangles indicate ongoing trends. Upward triangles mean a stock should continue to go up. Downward triangles mean downward trends will ...

In the graph above, although there is not a straight line increase in figures, overall the trend here is that sales are increasing.