[rrd-users] Re: --width affects results?

Alex van den Bogaerdt alex at ergens.op.het.net
Tue Oct 4 13:40:01 MEST 2005

On Tue, Oct 04, 2005 at 10:20:11AM +0200, ralf-buero at kruedewagen.de wrote:

> > I'm sure a thourough analysis would explain the differences.
> > For research, see footer.
> Yes, this is what I have already assumed during my studies. Even if 
> you use GPRINT, the results are also different depending on image 
> size. The results differ for me much more than in Grishas example 
> (for instance 98.1 vs. 96.0).

It is not the image size itself that causes different data.

If you have one-hour data available, and ask for 00:00 to 24:00,
you get 24 rows of one hour each.

If you have one-hour data available, and ask for now-24 to now,
you get 26 rows of one hour each unless "now" happens to be on
the hour exactly.  This is because you ask a different question.

> The big problem is: How can I calculate a mathematically correct 
> average now based on all measurements between start and end time ? 
> Nobody (if not knowing the details of RRDtool) will trust me, if I 
> say, that averages (numbers) depend on the size of the image. The 
> size of the image should IMHO not affect numbers calculated and 
> printed by GPRINT or PRINT.

You do not have a correct result if you do not start with correct
assumptions.  From what I read here, you don't.

Alex van den Bogaerdt

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