Thanks again. So, I guess my original assumption was more or less correct. I've never seen that on any other diagram before and I couldn't find any explanation for it on the diagram itself. I'll be diagnosing a board today and I'll put this theory to the test.

Thanks for the reply, and I know what you're referring to, but that's not it. These numbers all have little arrows (more like tiny triangles, really) pointing directly to pins on chips or specific connections in the diagram. The pin numbers themselves are present in little circles at their locations...

Hello everybody, you've got a really nice site here with tons of useful information. But there's still one thing I couldn't find. I've got many, many years of experience with wiring diagrams, but the PSOne board schematics have little red numbers with arrows pointing to most of the pins on the chips...