 When I take biology classes, I'm assigned big chunks of textbook readings every week. Some of the ideas in these readings are new, while others are familiar ones I've already seen before. To save time and increase efficiency, I vary my reading speed. When reading about the nervous system, basic neuron anatomy is usually covered. I could skim through that because I have seen this information several times. But when the book dives into the action potential in detail, like the sodium-potassium channels, I should slow down and read closely to understand all the steps.