Range indicators that visually convey values
The objective for all presenters is to present concepts visually that are both visually descriptive and aesthetically appealing. It's important to make every element on a slide support that objective. Sometimes that requires thinking beyond what is typically used (two-way arrows that show direction only) and using a shape that illustrates an increase (right-triangle shape that shows volume growth).
The example on the left above is what is typically seen in presentations; but the example on the right is the better choice. The value can be understood even without the High and Low text labels. The right triangle conveys the less vs. more concept much better, however it is applied: more vs. less, low vs. high, etc.