The popular but older standards: PMC 22.1-1981, Functional Diagramming of Instrument and Control Systems; ISA 5.2-1976, Binary Logic Diagram for Process Operation; and ISO 3511, Graphical Symbols for ...

Scope Symbols are included to depict mathematical functions, graphs, process equipment, instruments, and electrical equipment. The symbols are suitable for use in dynamic displays, as on cathode-ray ...

Next to the master diagram, make a column of any rules that cannot be integrated into the diagram. However you want to express those rules, keep your symbols easy and consistent.