I have created a PE tag that is to provide the data results for a tag as a fifteen second total. Shouldn't the tag that the PE tag writes to have the same current value as the PE tag?

We are trying to evaluate the flow with a tag that returns the flow in cfm in real time. We have a tag that does that. We created a performance equation tag that takes uses the flow tag divided by 240 to give us the 15 second flow rate. The PE tag is supposed to write the 15 second total to a tag that has the same name but with an underscore FST added to the tag name. Shouldn't the Flow_FST tag return the same value as the PE_Flow tag?