[rrd-users] Plotting a derivative of gauge data

[Tobias Oetiker]

Hi Al,

Today Aleksandr Pasechnik wrote:

> Hello,
>
> I have some temperature data stored and I would like to plot the
> derivative to observe the rate of change. I can't seem to find
> anything along the lines of a derivative function in the rpn
> documentation. Can it be done? How might one go about calculating
> the derivative? I suppose a simple diff would work, if I took the
> stack, and subtracted a stack shifted by one it would give me
> what I need, but I was hoping for a built in function of some
> sort.

the easiest way of doing this is to log the data twice, once as
GAUGE and once as DERIVE type.

todo it on the fly you may be able to do something using the PREV
function ...

cheers
tobi

>
> Thanks!
> Al
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Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland
http://it.oetiker.ch tobi at oetiker.ch ++41 62 775 9902 / sb: -9900