[rrd-users] absolute and relative graphing of the same value

[Karl Fischer]

Dear all,

I'm looking for a way to display a value in two ways without recording it twice:

Lets say I'm monitoring a typical GAUGE value like diskspace or temperature.

Now I want do display the temperature as an absolute value (=> GAUGE => 25C) *and*
I want to display (in another grapgh) the change rate (eg. +3C/h), which would
be a typical DERIVE application ...

I tried to use GAUGE and operate with rpn PREV, but since the temporary step-size
varys when graphing, I wasn't very lucky in calculating the right numbers ...

Here's the diskspace example - this doesn't always do what I want ...

--title=Used Disk Space - delta in Bytes/h
DEF:dfUsed=Space.rrd:dfUsed:LAST
CDEF:Btime=dfUsed,POP,TIME
CDEF:Btdiff=dfUsed,POP,TIME,PREV(Btime),-
CDEF:prev=PREV(dfUsed)
CDEF:delta=dfUsed,prev,-,Btdiff,/,3600,*
AREA:delta#7777ff

It seems to have some erratic behavior when changing the start/end time of the
graph and therefore the scale ...

Any hints for me?

Thanks

- Karl