Waterfall chart for open tickets

[shill1000]

​This is probably complicated but bear with me. The system we're pulling data from (into a SQL DB) cannot currently record the state of a ticket or who it is assigned to as a date related aspect. If the data is queried directly it will only reflect the current state.

To get around this we've created a table that writes off a record for every open ticket at the end of the day. This contains that date, the ID, state and assignment. I'm able to ascertain how many tickets were in each state and who they were assigned to on any given day by querying that day, at month end etc. What I am trying to work out is a how to get a waterfall chart to work showing the change in volume of tickets from day to day, for all, by state and/or by assignment. The issue I am finding is that although I can get a bar chart of the counts by date, using a hierarchy to only show the count for any one date. For month end, I can get a month on month count by using a flag to indicate if the date is last of the month and thus filter by that flag.

But when I try to do a waterfall, I get a cumulative count not a differential. I think I understand why this is happening; there is no numerical value to trend the change in volume by within the data. I assume the solution is a measure, but I'm a at loss to know where to start - my Dax skills are basic though I'm trying to learn as I go!