Issue finding hours since an event occurred using PI Vision.

Hi all,

I have been asked to return hours since an event has taken place in my process. There already exists an attribute that records start of the process. I am having an issue figuring out how to find how much time has passed from that point until now.

I attempted to replicate the solution here (Time Stamp for event) but I get an error in PI Vision reading 'Expression may not use functions that evaluate at different time contexts'.

FindNE('.\Agit|PV', '*-1d', '*', TagVal('.\Agit|PV', '*')) is the expression I attempted to use. I know the TagVal function is working correctly.

Am I able to achieve this in PI Vision or must I create a new attribute?