Numbers have to be read.

Numbers have to be read. Graphs allow you to see.

"Read" here means a kind of OCR, parsed into semantic understanding and then operated on. A multi-stage process.

"See" here means relying on the spatial intuition that happens in heavily optimized, deeper parts of our minds.

A quote from Poor Charlie's "At any rate, mankind invented a system to cope with the fact that we are so intrinsically lousy at manipulating numbers. It's called the graph. Oddly enough, it came out of the Middle Ages. It's the only intellectual invention of the monks during the Middle Ages I know of that's worth a damn. The graph puts numbers in a form that looks like motion. So it's using some of this primitive neural stuff in your system in a way that helps you understand it."