Teach the practical skills of using a scale correctly and measuring non-straight objects.
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Three key rules for accurate straight measurement.
Measurements begin with selecting the correct instrument. Use a rigid metre scale (or 15-cm scale) for straight lines and flat surfaces. Use a flexible measuring tape for measuring the girth (circumference) of objects like a tree trunk or a person's chest.
Diagram showing correct vs incorrect viewing angles.
Looking at the scale from an angle causes measurement errors. Always position your eye directly above the mark.
How to handle a scale with broken edges.
If the zero mark on a scale is broken or unclear, start from any full, clear mark (like 1.0 cm). Read the final mark, and subtract the starting mark to find the true length.
Math practice for broken scales.
You are measuring a piece of chalk using a scale with a broken zero mark. You carefully align one end of the chalk exactly at the 2.0 cm mark. If the other end aligns exactly with the 9.3 cm mark, what is the true length of the chalk?
How to measure non-straight lengths.
You cannot use a straight, rigid metre scale to measure a curved line directly. Things like the arch of a doorway, the rim of a bottle, or a squiggly line drawn on paper require a different approach.
Visual showing thread measuring a curved line.
A flexible string allows you to trace irregular paths and then measure their total length against a straight scale.
Match objects to the best measuring tool.
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