you have done well. may god reward your kindness to human kind. your effort saves many aspiring planners a lot of money and time in training costs.

i’m just a little bit confused with your question. but anyway let me help you in my own understanding of your question. first, cumulative is accumulation of units/quantities over time. what i understand is that your given units/quantities are referring to the periodic plan and actual. if that is so, it is recommended to use the column (highly recommended ) or bar chart to see the difference between the plan and actual. in cumulative plan and actual, it is just a comparison if you are right on plan, above the plan, or below the plan. in your curve, if the actual is above the plan, then you have a positive variance, if the actual is below the plan, you have a negative variance, if the actual is in same line with the plan, then you have 0 variance.
hope this helps you.