Sum of values that aren't in units by time

Hello:

We're working on some pacing charts for a casthouse.

I have a tag that gets updated via RBDMS everytime we complete a coil. This tag contains the # of good pounds in that coil.
This is usually around every 29 mins or so, but it can vary.

I'd like to sum the individual values across a shift, The issue i'm running into is the values aren't in units per second,hour, etc. So I'm struggling with PE or Totalizers.

I've mostly worked on the interfaces and admin before, So the calculation engines are a bit new to me.

Would someone be able to point me in the right direction?

Thanks,
Michael