Tidal range is the difference in height between high and low tide, as explained in NOAA’s introduction to tides. A small arithmetic example can make the term clearer without turning it into a navigation calculation.
Keep both heights on the same basis
Imagine a teaching example with a high-water height of 4.2 metres and a low-water height of 1.1 metres, measured relative to the same reference level. The difference is 3.1 metres. The figures are invented and do not describe conditions at a real harbour.
The shared reference matters. Subtracting values expressed in different units or relative to different datums would not give a meaningful result without the appropriate conversion and context.
Separate the definition from passage planning
This range does not tell you the water depth at a particular location, the current speed, or a safe time to pass an obstruction. Those questions require current, location-specific information and appropriate navigational competence.
For a learning notebook, copy the definition, the labelled example, and one question about a real table you are studying. Use official local information and qualified instruction for practical decisions. Understanding a term is a useful step in learning to sail, but it is only one part of reading the changing coastal environment.