Unit 1 General physics
Section 1.1 Length and time
When making measurements, physicists use different instruments, such as rulers to measure length, measuring cylinders to measure volume and stopwatches to measure time.
A ruler is used to measure length. When using a ruler, be careful to avoid parallax error.
Parallax causes an object to appear shorter or longer depending on how you view it. An object must be viewed at right angles to the scale to measure its length correctly.