Explicit filter argument of Calculate function : Not able to understand its evaluation

ARU_ Since marcorusso wrote the explanation for CALCULATE's internal wiring, perhaps he might drop by and explain where you are going wrong in your interpretation of things. However, I believe where you might be not understanding things is that the CALCULATE expression is being evaluated for each row within the SUMX. It is not independent and does not come "first". Thus, for Katie Jordon, when the CALCULATE determines the LASTNONBLANK, it is finding the LASTNONBLANK within the context of Katie Jordon. The same is true for the other individuals. It is not that the LASTNONBLANK fires and returns the last date where the COUNTROWS is blank for ALL of the people, it is always scoped to each individual. Hope that makes sense.