Stacked Area Line Chart with Overlapping Values

Question

I'm trying to create an attendance chart. Previously, there was only 1 time slot, so I used a line chart. However, now there are 2 time slots. So, I'd like to do a stacked area line chart to summarize both individual and total attendance between both time slots. The problem is that some attend both time slots. I don't want the total attendance for the day to be skewed (i.e. total number of people in attendance), nor do I want the attendance for each time slot to be skewed.

How can I track the attendance accurately and represent it on the chart? Is there some way I can specify an "overlap" in attendance (i.e. 100 at time 1, 100 at time 2, 25 at both, for a total of 175 for the day)? Here is an example of one day of data:

Answer 1

Apparently you want to plot attendance vs date, which wasn't clear.

Set up data as shown, with dates in the first column, then attendance in the first time slot only, attendance in the second time slot only, then attendance in both time slots.

Make a chart of this data. I show a stacked area chart, but I prefer the stacked column chart.

EDIT:

Here's how to do an overlap with Area Charts. Arrange the data as shown, with total for each time slot, and in between the negative of the number of people common to both. Make your area chart. Format 9:00 AM as blue, but with 50% transparency. Format 9 & 11 as no fill. Format 11:00 AM as orange with 50% transparency.

Since the 9 & 11 series is negative, it moves down from the previous (9:00 blue) series, and the next series (11:00 orange) starts from the lower position. Where there is no overlap, the orange just seems to start at the top of the blue. And you can use your own colors that might show the overlap more clearly.