Cumulative Total

Good morning All,

Looking for some help with calculating a cumulative measure.

Tha data I am working with is here: https://www.dropbox.com/s/y47316tmtlmzbet/Cotton%20Purchases.xlsx?dl=0

The data is for 2017 & 2018.

I wouldlike to come up with cumulative measure based on trading day and not date (you will see that the dates start at different points in 2017 as compared to 2018)

I need to be able to draw a cumulative line chart that shows cumulative purchases by trading day so that for example I can see what cumulative purchases by day 11 were in 2017 compared to day 11 in 2018.

Hope this makes sense, if not I can clarify.

Many Thanks

Herbz