Figure 17–44 is a photograph of a computer screen shot by a camera set at an exposure time of $\dfrac{1}{4}s$. During the exposure the cursor arrow was moved around by the mouse, and we see it 15 times.

VIDEO TRANSCRIPT

This is Giancoli answers with Mr. Dychko. The computer screen is redrawn 14 times during this one quarter second. And plus there is the initial position of the cursor for a total of 15 cursor positions. And what you're seeing here is like a strobe like a fact where you know the cursor movement it looks continuous. When you look at it with your eye but the cursor is actually jumping from position to position. Each time the screen is redrawn and since it's a 14 redraws and one quarter of a second the refresh rate is 56 Hertz.