[rrd-users] Get DS:MAX without MAX RRA

[Matt Elias]

I would like to display two data definitions on one graph, temperature 
and humidity. I would like to get the main Y axis (temperature) scale to 
remain automatic (or manually set a little lower than the min and a 
little higher than the max) and the right axis (humidity) scale at the 
same scale (ie 0 - 100). My initial thoughts are that if I can get the 
graph's min and max temperature values, then maybe I can use that to 
scale the Y axis and use a formula to scale the humidty values 
accordingly so that they match the right axis' 0-100 scale. The min and 
max values I need are similar to the MAX and MIN values that are 
displayed in the GPRINT paramenters:

         "LINE1:Temp#32CD32:Temperature C",
         "GPRINT:Temp:MAX:  Max\\: %5.1lf %s",
         "GPRINT:Temp:AVERAGE:Avg\\: %5.1lf %s",
         "GPRINT:Temp:MIN:Min\\: %5.1lf %s",
         "GPRINT:Temp:LAST:Last\\: %5.1lf %s\\l",

If something like this is not doable from within RRDtool, then I may log 
additional data to a log file and have my graph generating perl script 
use that log file to manipulate the Y axis scales.

Matt