I have a chart that summarizes survey responses:
- Y axis is the percent of total respondents
- X axis is the Likert scale responses, "Strongly Disagree (1)", thru
"Strongly Agree (7)".

I want to add a vertical bar that shows the average response (which the
chart would take from the spreadsheet).

For example, if the average was "5.5", I want the bar to be vertical, and
for it to cross the X axis where 5.5 would fall, between the "Somewhat Agree
(5)" and "Agree (6)" bars, as if the X axis were truly a numerical plotting
(as opposed to the text responses).

I suspect it is a secondary X axis without displaying the scale, but I
cannot seem to make it work. Help! Thanks VERY much!