D as a Nashville Chart Sees It

Count off in D and the seven numbers name D, E, F#, G, A, B, C# — in that order, every time, on a page that never mentions D anywhere.

Three of those need a mark and four do not. A bare number is a MAJOR chord, so 2-, 3-, 6-, 7- are what a chart writes when it wants the chord the key would have supplied anyway; a bare 2 means the writer wanted something else and meant it.

A guitarist reads a shape per number — the one hand position that has to be found before the bar arrives, which is why a guitarist reads a chart one bar ahead of everybody else. The chart hands over a degree and nothing else, so the hand has to arrive at a whole shape from a single digit, and it has to have arrived before the bar does.