# [mrtg] Re: How does it get those funky numbers?

Matt Katona mkatona at comwavz.com
Mon Jul 22 15:31:48 MEST 2002

```Thanks Paul!!!

So in a nut shell:

MRTG reads the counter for an OID and records it (ie: 1000) and plots it on the graph
MRTG sleeps for five minutes then reads the counter again,  (ie: 2500). Now MRTG subtracts 1000 from 2500 and plots 1500 on the graph.
MRTG repeats step two every 5 minutes.

MRTG reads 6 polls in 30 minutes, adds all the entries up and divides by 6.
MRTG plots/records the 30 minute average.

MRTG takes the last 4 average 30 minutes polls in two hours, adds all the entries up and divides by 4.
MRTG plots/records the two hours average

MRTG takes the last 12 average 2 hour polls in 24 hours, adds all the entries up and divides by 12.
MRTG plots/records the Daily average

Anything else you think a suit might like to see?

-----Original Message-----
From: PAUL WILLIAMSON [mailto:pwilliamson at mandtbank.com]
Sent: Monday, July 22, 2002 9:07 AM
To: Matt Katona; mrtg at list.ee.ethz.ch
Subject: [mrtg] Re: How does it get those funky numbers?

First item is incorrect.  MRTG just pulls the number.  The first number plotted is
the DELTA of poll 1 and 2.  To get averages, it does it like this:

It gets 6 polls in 30 minutes, so it adds all the entries up and divides by 6.
Voila!  There's your 30 minute average.

How it does the monthly (2 hour) averages or the yearly (1 day) averages
is really averages of averages.  Since the 5 minute polls don't exist
for longer than 400 polling intervals, that's how it gets those averages.
In your example, 1500 would be the first entry in the database.

Don't forget normalization.  More than likely, you will not poll the device at exactly the same interval, so MRTG makes allowances for that.

Paul

>>> "Matt Katona" <mkatona at comwavz.com> 07/22/02 08:40AM >>>

Ok, management is asking about how MRTG pulls it's numbers. This is how I understand it (i'm looking for correction/clarification)

MRTG reads the counter for an OID and records it (ie: 1000) and plots it on the graph
MRTG sleeps for five minutes then reads the counter again,  (ie: 2500). Now MRTG subtracts 1000 from 2500 and plots 1500 on the graph.
MRTG repeats step two every 5 minutes.

But how does the "average" get calculated?

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Matthew Katona
ComWavz
Systems Engineer
O:419-859-2194 x1771
C:419-460-1776
http://www.comwavz.com
"Consistency is the last refuge of the unimaginative" tagged by Oscar Wilde (1854-1900)

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