I have a list of times in one column formatted as hh:mm:ss. Some of the
cells are blank because there was no time associated with a particular task.

I'm trying to sum and ultimately average these numbers. Everytime I try I
get 00:00:00. I've tried formatting both the column and my calculation to
[hh]:mm:ss and that doesn't appear to work. The only thing that works is
adding each value individually. I can't do that as there are thousands in my
list. Little help?