When you take a measurement, there is an actual value that you are trying to measure. This actual, real-world, value you are trying to measure is called the true value.

As an example, there is a true length of the toy van below, and we use the ruler to take a measured length. Assuming that the ruler has been set up correctly and the scale read properly, the measured value should be very close to the true value.

Note: You will never know the true value, you can only make efforts to take the best measured value possible.

As another example, in the image below, there is an actual, true, angle between these two lines, and the protractor is being used to try and measure this value. Assuming that the protractor has been set up correctly and the scale read properly, the measured value should be very close to the true value.