[rrd-users] Re: PREV fails?

[Tobias Oetiker]

Today you sent me mail regarding Re: [rrd-users] Re: PREV fails?:

*> Tobias Oetiker wrote:
*> > 
*> > Today you sent me mail regarding Re: [rrd-users] Re: PREV fails?:
*> > 
*> > *> Duh, it seems that the outcome of PREV is not related to the DS.  It is related
*> > *> to the outcome of the previous CDEF value.
*> > *> I seem to have misunderstood the manual.
*> > *> 
*> > *> Can somebody confirm this please?
*> > 
*> > oops yes sure, because otherwhise which DS would PREV refer to ?
*> > 
*> 
*> I tried something like:
*> 
*>    DS:t=blah.rrd:usertime
*>    CDEF:tt=t,PREV,-
*> 
*> In other words, I tried to work with the difference between the
*> previous value and the current one.  Obviously, it doesn't work this way.
*> 
*> I'm sure I'll work around this sometime.

this will work, but you must guard against getting any unknowns in there ...
at first PREV will be UNKNOWN. This will propageat ... 

cheers
tobi
*> 
*> regards,
*> 

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