Measurement
How do you put a number on how long, how heavy, how hot or how much space something is, so that anyone anywhere can check it?
Where you are 12 inside
What this area is about
To measure is to pick a unit and count how many copies of it fit. That one idea runs through every measurement: length, area, volume, mass, angle, temperature and time. This area builds it from comparing two objects by eye up to converting units and judging how many digits to trust.
How these fit together
The foundation. What measurement is covers comparing, units, reading a scale and how exact a reading can be. Systems of units covers the customary and metric families and how to convert between any two units.
One attribute each. Length, area and perimeter, volume and capacity, mass and weight, angles, temperature and time and money.
Built from measurements. Rates from measurements divide one measurement by another. Scale and size tracks lengths, areas and volumes when a whole object is scaled. Reasoning with units uses units to set up and check a multi-step problem.
A path through it
Start with the early lessons of what measurement is; its later lessons, length, mass, volume and systems of units interleave, each needing parts of the others. Area follows length, and volume follows area. Angles and temperature follow what measurement is. Time and money can run alongside. Mass follows systems of units. Rates come after mass, volume and time; scale and size after angles and volume. Reasoning with units waits for both foundation areas (it is grade 9 work).
Next: angle pairs, the area of a circle and the Pythagorean theorem.