Rulers, measuring jugs, weighing scales and thermometers all show numbers along a line of marks. Usually only some of the marks are numbered, with smaller marks in between. To read one off, you first have to know what one small mark is worth.

Pick two numbered marks, subtract to find the gap between them, then divide by the number of small gaps in between. For example, between 0 and 10 with 5 equal spaces, each small mark is 10 \div 5 = 2. Now just count on from a numbered mark, two at a time, until you reach the pointer.

If the pointer lands exactly on a mark, read it straight off. If it stops part-way between two marks, estimate — about halfway between two marks worth 2 each is roughly one more, so one unit past the lower mark.

Reading a pointer

Here the numbered marks 0, 10, 20, 30 have small marks every 2 units. The pointer sits 2 small marks past 20, so it reads 20 + 2 + 2 = 24.