What number should be on the left side rail of a wiring diagram?

In a wiring diagram, the left side rail typically represents the first vertical line of the schematic, and it is used for indicating the reference number for the corresponding circuit or section. This is crucial for identifying the various components and their positions in relation to the overall diagram.

Having the number 1 on the left side rail designates it as the primary reference point for that particular part of the diagram, thereby allowing technicians and engineers to easily follow and interpret the sequence of circuits and connections. It acts as a starting point for understanding the flow of electricity through the system. Ultimately, this numbering convention is rooted in common practices for clarity and standardization in electrical schematics.