If you put a chart in front of someone with all sorts of instructions, the playing becomes 'robotic'. I've dictated charts to my wife in the car en route to gigs before - hers turn out way neater than mine. I like it mainly because I don't need a pitch reference to chart, so I can chart on airplanes or whatever. The only exceptions are tunes with crazy jazz harmony, indistinct/shifting tonal centers, or super-intricate parts that must be nailed exactly. I chart pretty much everything Nashville style these days. I would indicate the key of the tune as "C (Am)" up in the corner of the chart, and notate the verse as 6 2 4 5. So for example - verse is in A minor, progression Am-Dm-F-G. I don't want to bother to scan all the way through the tune before I start charting to find out whether it goes to the relative major or not, so I just assume it will. If I'm charting a tune that starts out in a minor key, I will usually notate it as though it were in the relative major, because with pop or country tunes it will almost always will go to the relative major in the chorus or bridge, and then it becomes a pain (for me anyway) to read/write that section correctly. Minor keys are another thing that some folks tend to handle differently. If it needs to be indicated, then personally I use - for minor and + for major - faster to write and easier to distinguish. minor if a chord is going against the "normal" (diatonic) voicing. When I'm Nashville charting, I'm usually doing my darndest to get a finished chart in one real-time listen through the song, either because I'm at a session, or I've got 39 more songs to chart after this one. And yes, Arabic numerals are definitely the way to go.
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I agree with both of the interpretations above. The fact that it includes sample charts from several different musicians is really helpful, considering that it tends to be a highly personalized thing from one player to the next. The Chas Williams book is a worthwhile investment.