Our class puppet just measured a pencil and proudly called out the wrong length. The puppet started at the plastic end of the ruler, before the 0 mark. Hands up: what did the puppet forget?

The puppet put the plastic end of the ruler at the start of a line. The line is really 6 cm, but the reading looked like 7 cm. That is wrong, because the 0 mark was not at the start.

When 0 sits at the start of the same line, the far end meets 6. Missing the 0 makes every reading too big by that same little gap before the 0.

Next check: keep the ruler straight along the ribbon — no tilt.

Last check: read the number at the far end. That number is the length in centimetres.

Let's read a length together on the board. One pupil at a time moves the reading mark to the end of the line. Before we agree, we say our checks out loud: 0 at the start, ruler straight, read the end. What length is this line?

We read each length on the board together. Before every Check, say the habit out loud: 0 at the start, ruler straight, read the end. One pupil moves the reading mark; the class agrees the number.