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)?

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: