## Learning Outcomes

After completing this module you should be able to:

**Use appropriate units**of length for different measurement contexts (milli-, micro- and nano- worlds)**Convert units**of length

## Tall (and small) fish tales

How big is a fish? Ask a fisherman and he will tell you it was as big as his outstretched arms. Ask his friend and he will hold up his forefinger and thumb and say “it was this small”…… But what is the truth and how can you be sure of the actual size of the fish?

From your primary schooling and everyday experience you have an intuitive sense of measurement and this is used to standardize measurement for everybody, no more tall stories about the size of a fish! We can put a physical size to the fish that everybody can understand.

From your everyday life, you have an intuitive sense of what a centimetre, metre, and kilometre look like.

Now that youre studying biology, **you need to develop the same intuitive sense of what a millimetre, micrometre and nanometre look like**.

The hard part is that, while we can see a centrimetre, things that are on the order of millimetres are kind of small, things on the order of micrometres can rarely be seen directly, and nanometres you might as well forget seeing them without a really good microscope.

Nevertheless, were going to try to divide up the biological world into these scales and do what we can. Before we start, it will be helpful to have a ruler (or anything else that can easily measure millimetres) and a calculator on hand.