# [rrd-users] What type to use?

Yiannis Vavouranakis yiannis at vavouranakis.gr
Sat Feb 27 02:12:20 CET 2010

```Hello list.

I have the following problem.

I have a variable number of people in a room. I check who is in the room
at regular times, and I get the time spent in the room so far per
person, among other things. These "other things" (like the total number
of people in the room as a timeseries) dictate that I should use rrdtool
to efficiently collect and display any information related to these people.

Currently I'm in a pickle, because I need to know the "total" time spent
in a room by all, as well as the average time spent in the room.

An example may clear things up regarding the "total" and "average" time:
Assume the following results when I do three consecutive checks, each 5
minutes apart from the other:
Check 1: 2 persons, one is in for 60 minutes, one is in for 17 minutes
Check 2: 1 person, in for 22 minutes
Check 3: 2 persons, one is in for 27 minutes, one is in for 3 minutes

What has really happened, is that the person who was in for 60 minutes
when I first checked, decided to leave sometime between the first and
the second check, another one was in the room (and never left) during
all three checks, and another one (who may or may not be the same as the
first one, I don't care about that) decided to enter the room 2 minutes
before check #3.

I need to know the average and total time spent in the room by people
that were present anytime within the time period specified. For example:
- a period including only check#1 and check#2 should give (60+22)/2=41
minutes average time and (60+22)=82 minutes total time.
- a period including all three checks should give (60+27+3)/3=30 minutes
average time and (60+27+3)=90 minutes total time.
- a period including only checks #2 and #3 should give (27+3)/2=15
minutes average time and (27+3)=30 minutes total time.

Is this at all possible with RRD?

Regards,
Yiannis Vavouranakis

```