[rrd-users] Working with linear slope calculations

Simon Hobson linux at thehobsons.co.uk
Tue Jan 22 17:43:47 CET 2008

A Darren Dunham wrote:

>  > If you need to convert within the graph, then simply plug in the
>>  correct figures to an RPN expression, eg :
>>  t=p,400,*,86400,/,s,+
>>  Given p as the number of pixels found from some other calculation,
>>  400 & 86400 are the graph width and duration as given in the graph
>>  command, and s is the graph start time (also given implicitly or
>>  explicitly in the graph command); then t is the time you are looking
>>  for.
>That's the bit I'm trying to avoid.  It seems like I have to hardcode
>the size of the graph within a calculation.  That makes changing things
>significantly more complex.

Only if you hardcode your graphs. I generate my graphs from scripts, 
so the 400, 86400, and s would already be in variables to start with. 
Eg, in shell you might write :

echo "... p,${gw},*,${gt},/,${gs},+" >> somefile

I'm assuming here that p comes from the slope function your trying to 
use and so is already known to rrdtool.

>From your suggestion, I take it there's no
>way to poll for those values directly?

Not that I know of.

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