Some measurements, such as the length of the index finger, are relatively straightforward but others, such as the length of the thumb, are not, as there is no obvious place where the thumb stops and the palm starts. This should give rise to a discussion about how reliability and validity of measurements can be obtained. Students can repeatedly roll a ball down an incline onto some carpet and measure how far the ball rolls. Theoretically it should give a nice normal distribution. Working in groups, students in the class can use a beam balance to measure the weight of a full can of coke, and a graphical display of the set of measurements can be produced.
Students can count the number of beans in a cup of beans.
And so on. Slope is pi. Hang spring on support. Add a weight and measure the stretch. Constant slope is spring constant.