### 4.2.4 Word equation

Many modellers suggest that as a preliminary to writing down a mathematical model, that is, a mathematical equation, the modeller should always try to write down a word equation. This is probably a good idea since modellers should always be able to communicate their ideas both to fellow modellers, often mathematicians, and also to non-mathematicians who may need to use the model predictions ultimately obtained.

A word equation describing the model that we now have could be:

Over a unit time period, the fish population exhibits the following relationship:

Population at the end of the time period is equal to the population at the start of the time period plus the number of fish resulting from births minus the number of fish resulting from natural deaths.