Testing a square corner

A carrom board has a damaged corner. Is the corner still square?

The rule

Two lines that meet at a square corner are perpendicular. The turn between them is 90°, ninety degrees. Each line is called an arm of the corner.

Mark 30 mm out on each arm. The mm means millimetres. Measure the gap between the two marks. A square corner gives 42 mm.

A square corner leaves a 42 mm gap for 30 mm marks. Make the corner wider and the gap grows. Make it narrower and the gap shrinks.

Example

Marks 30 mm out. A square corner would give 42 mm. The gap reads 46 mm.

46 is more than 42. So the corner is wider than square.

Try the lab to finish this lesson.