Thanks but this sheds very little light on the issue. I already read the section you refer to and it provides scant detail / examples. Very verbal no visual. In some charts virtual columns may not be used for the x-axis in other they may. Some may allow drill down others not.
I understand the charting is canned but is somewhat primitive in terms of options so any (programming and non-programming user) needs to understand both the context and extent to which the provided Appsheet charting options may be used or cover.
Otherwise it turns into a mass bang your head manual exercise.