The key idea of measurement at level 2 is that units can be used to measure objects.
The key idea of measurement at level 3 is that the attributes of an object can be measured against a standard scale.
The key idea of measurement at level 4 is the application of multiplicative thinking to measurement.
The key idea of measurement at level 5 is that all measurements are approximate. Because measurement involves continuous quantities even the most accurate measurements are only approximations. As students develop their ability to measure a variety of attributes using a variety of units, they need appreciate that measurements are never exact, and that all measurements contain errors. For any measurement, the level of precision required will depend on the way the information is going to be used. For example, when purchasing fertiliser the number of litres required is probably sufficient but when purchasing medicine the number of millilitres required is likely to be more appropriate. At level 5 students are also able to split complex shapes into component parts in order to calculate their length, area, or volume. For example, the surface area of a cylinder can be calculated as sum of the area of two circles and a rectangle. At this level students need to develop the ability to compose and decompose shapes in order to find the lengths, areas and volumes of various complex objects.
The key ideas measurement at level 6 are the concept of the accuracy of a derived measure and the understanding that abstract mathematical formulae may be used to solve problems. Accuracy of measurement is an important element in measuring. It is important to know both how accurate a derived measure needs to be and how accurate the measuring device can be in a given situation. Similarly, accuracy specified in terms of number of significant figures allows students to see equivalence of levels of accuracy within different metric units. For instance, there is no difference in the level of accuracy between 4.80 metres and 480 centimetres even though one may appear to be more precise than the other. At level 6 students are also able to apply formulae relating to simple three-dimensional figures. This enables unknown dimensions of common objects to be determined. Because of their difficulty these formulae may be introduced without proof or formal derivation in order for them to be used to solve problems. So now students need to know how to use, and understand the relevant parts of a formula and they also need to know how to select the appropriate formula. This may mean checking a formula’s dimensions so that, for instance, they do not use an area formula to measure volume.