Many people struggle to learn Secondary Ports but this simple graphic method shows how simple Secondary Port Calculations can be. This A4 encapsulated sheet will make life so much easier.
Side one explains how the information that you need is laid out and what that information means, as well as a worked example of Time Differences. Side two has a worked example of Height Differences with plenty of space for your own calculations.
Matt encapsulation means that a 2B pencil may be used directly on the plastic.