1. There are two versions of the Tarrant rule. The one shown here - which is a duplex rule with pipe flow calculations on one side and open channmel calculations on the other - and a simplex rule - which only has the pipe flow calculations.

2. This version of the rule was produced by BRL for promotional purposes for Paterson Candy International who, among other water related activities, sold pipes.

3. A copy of the instructions (covering both types of rules) is given here.