Aggregating Averages and Standard Deviations

[ThePeterK]

This app is calculating our progress towards a goal of billable hours running up to the start of a new fiscal year.

I've got to aggregate the averages of each pct to goal for each FY across a 'Snapshot Period' and return the raw numbers, averages, pct to goal, and the standard deviation for each snapshot period. I'm having issues getting a standard deviation of the percent to goal across each snapshot period.

The average (mean) function appears to work fine:
AGGR(nodistinct sum({<STATUS_DESC={'Requested','Completed'}>} REQ_HRS),SNAPSHOT_NAME)/
AGGR(nodistinct sum(HOURS_GOAL),SNAPSHOT_NAME)

There is an additional dimension for "Fiscal Year" that I need to add to the above, but I can't get it to work even without that dimension in the mix. 

Aggr(Stdev(AGGR(sum({<STATUS_DESC={'Registered','Complete'}>} REQ_HRS),SNAPSHOT_NAME)/
AGGR(nodistinct sum(HOURS_GOAL),SNAPSHOT_NAME)),SNAPSHOT_NAME)

Any ideas?