Timeline slicer, Calculate value between two dates + nulls

[Andrewstg]

So I am trying to get enrolled students between 2 dates and a null using the Timeline slicer and I am having a bit of trouble.

So here is my table, that I have joined on a calender to Startdate. https://imgur.com/a/rRODk,

What I need to do is when the timeline slicer is between start and graddate  it adds +1 count or even sum +1

If  a student has a startdate and grad date = null then it should also add a +1 when timeslice is >= startdate.

Here is a view of my relationships. 

https://imgur.com/a/jQvSz.

I have created a new start table, grad and enrolled all linked to the Calander.

[Eric_Zhang]

@Andrewstg

What is the +1 count and +1 sum? Could you post some sample data and expected output?

[Andrewstg]

Yea no problem, so I need to use the timeline slicer as the date range to count which students were enrolled at the time.

So if I have a start date but no grad date as in Grad date = null then he is enrolled from Startdate to Current Date and is +1 to the count during that time frame when selected on the timeline slicer. 

If they have a grad date then I need the timeline slicer to be from startdate  to grad date = +1 to the count for enrolled.

Since its only +1 I figured a sum or count would end with the same results.

Maybe using +1 is wrong but really jsut count students that fall between dates when using timeline slicer either Start to Curdate() when grad = null and start to graddate.