Reading a scale

Part of a number line is shown. Only six thousand and seven thousand are labelled, and the marks between them are equally spaced. What number does the arrow point to? Try it first. Pause if you like. The same number line can help us count the gaps. The marks are equally spaced. Count the gaps between the two printed numbers. One. Two. Three. Four. Five. There are six marks. But only five gaps. Count gaps, not marks. The number of equal gaps is five. One gap is seven thousand minus six thousand, divided by five. One gap is two hundred. The arrow is three gaps along from six thousand. Start at six thousand, and add three times two hundred. Six thousand, six hundred. Find how many equal gaps are between the printed numbers first. One gap has one value, and every gap on the line has the same one. So start from the number printed before the arrow, count on one gap at a time, and that is the reading.