summation of volume based on time not bars

["Dean DiCarlo" <junkmayl@xxxxxxxxxxxx>]

I want to design a function to sum the last hour of volume data for each
symbol on my radarscreen.  I started using summation(v,60), but i found out
quickly that with stocks that don't trade often, it was summing the last 60
bars of volume data rather than the last hours-worth of data.  is there a
way to sum volume data based on time rather than bars?