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One of the most famous problem solving skill that we learned from school is "divide and conquer", i.e. to break down larger problem into several smaller problems, and solve it one by one. This can be also applied to reading.
After some training, you can speed up your reading by just focusing on the current block of text, rather than on the page, or paragraph. By using line number, we can count / jump easily.
This tool is highly configurable and you configure the height, color, style and margin of the gridlines.