How are the of plain scale and diagonal scale used?

A plain scale is used for measuring distances on maps or plans, typically representing a fixed ratio where each unit corresponds to a specific measurement in real life. It provides a straightforward way to interpret distances without complex calculations. In contrast, a diagonal scale is more advanced and allows for measuring lengths with greater precision, incorporating both the main scale and additional divisions. This is particularly useful for representing smaller distances or fractional measurements, making it ideal for detailed engineering or architectural drawings.