Approximation of Hourly Census

[Anonymous]

Hi,

I am trying to approximate a 24 hourly census in a bar chart using the following expression:

=Round(avg(aggr(Sum(CensusIn),CensusHour,VisitDate))

+ avg(aggr(sum(EDTime),CensusHour,VisitDate))/2

- avg(aggr(sum(CensusOut),CensusHour,VisitDate)))

Its a pretty good approximation, but if I filter on a specific day, it quite a bit off.

Any ideas?

Thanks,   Jonathan