Local maximum and minimum

Hello,

I have a 1-wire setup in my attic.  I log temperature and humidity and 
generate daily/weekly/monthly graphs.  I use a modified temps.pl from 
Thierry Hugue.

What I would very much like is to graph the local maximum and minimum 
temperature.  This would be roughly the maximum and minimum over a 24 
hour period.  The MAXIMUM and MINIMUM operators don't do what I want - 
they find the max for the entire period.

Is this at all possible with RRD graphs?  Or do I have to create another 
data set and calculate it by hand?

-Philip