gprof disagrees with time

[Nicholas R. Markham]

I'm using gprof to optimize some software I've written and I'm seeing 
something strange happen.  When I use time to measure the the running time 
of the program, I get about 6.4 seconds, yet gprof claims the total is only 
2.0 seconds.  For comparison purposes, I compiled the same program without 
the -pg flag, and the running time was about 5.7 seconds.

Am I misunderstanding what gprof is reporting?  Shouldn't the total of the 
times spent in each function be roughly the running time of the program?

Insight appreciated.