# [rrd-users] problem calculating the difference between MAX and MIN

Yannick Marquet itcsoft54 at yahoo.fr
Fri Jun 28 00:14:04 CEST 2013

```Hello,

rrdtool is a tool to store normalized value, and aggregate data over
- http://www.vandenbogaerdt.nl/rrdtool/ Section "List of tutorials and
the like".

In your rra, you store only MAX values for each step, so data collected
is normalized using MAX function (see
http://www.vandenbogaerdt.nl/rrdtool/min-avg-max.php).
So you can only work with MAXIMUM of MAX, AVERAGE of MAX and MINIMUM of
MAX. Because you keep all collected step in you RRAs, using CF MAX,
AVERAGE or MIN get same data stored.

I understand you want to display MAX value in graphed curve, MIN in
graphed curve, AND MAX-MIN in graphed curve, independently of RRA CF
function used to stored data.

http://oss.oetiker.ch/rrdtool/forum.en.html#nabble-td7580778

A Solution can be :

rrdtool graph VSM.png --start end-24h --end now ^
--title "Aktueller Stromverbrauch" --width 600 --height 330 --alt-y-grid
--slope-mode ^
--upper-limit 5000 --lower-limit 0 --rigid ^
--color BACK#A9F5F288 --vertical-label "Verbauch in kW" ^
DEF:Watt=VSM.rrd:Watt_cur:MAX ^
LINE1:Watt#FF0000:"Verbrauchskurve" ^
VDEF:Wavg=Watt,AVERAGE ^
VDEF:Wmin=Watt,MINIMUM ^
VDEF:Wmax=Watt,MAXIMUM ^
VDEF:Wact=Watt,LAST ^
DEF:kwhx=VSM.rrd:Watt_tot:MAX ^
VDEF:kwhmax=kwhx,MAXIMUM ^
VDEF:kwhmin=kwhx,MINIMUM ^
CDEF:delta=kwhx,POP,kwhmax,kwhmin,- VDEF:dd=delta,LAST ^
COMMENT:"\l" ^
COMMENT:"Verbrauch max      " GPRINT:Wmax:"%%6.2lf [W]\l" ^
COMMENT:"Verbrauch min      " GPRINT:Wmin:"%%6.2lf [W]\l" ^
COMMENT:"Verbrauch          " GPRINT:Wavg:"%%6.2lf [W]\l" ^
COMMENT:"Zaehlerstand max   " GPRINT:kwhmax:"%%6.2lf [kW]\l" ^
COMMENT:"Zaehlerstand min   " GPRINT:kwhmin:"%%6.2lf [kW]\l" ^
COMMENT:"                   " GPRINT:dd:"%%6.2lf [kW]\l" ^
COMMENT:"Verbrauch aktuell  " GPRINT:Wact:"%%6.2lf [W]\l"

Best regards,

Yannick

> Hello Yannik,
> thank youz for your quick response,
> I am new to RRDTOOL
> but this is a great tool...
>
> this is my create command:
> rrdtool create c:/rrdtool/VSM.rrd --start \$epoch_start --step 10
> DS:Watt_cur:GAUGE:60:U:U RRA:MAX:0.5:1:60480 DS:Watt_tot:GAUGE:60:U:U
> RRA:MAX:0.5:1:60480
> you are right, I have no RRA:MIN
>
> Could you point me to the right create command?
> I want to store two values
> 1. the current energy  in WATT ( this is a value from 0 to maybe >10000)
> 2. the current power in kWh ( this is a value which increases each time
> period)
> I want to show power and  delta energy in the graph ( which should be about
> 10kWh / 24h)
>
>   I want to show a second curevewith the delta of "Zaehlerstand max" and
> "Zaehlerstand min"
> and I want to "GPRINT" this value
> do I need to recreate the database?
>
>
>
>
>
>
>
>
> --
> View this message in context: http://rrd-mailinglists.937164.n2.nabble.com/problem-calculating-the-difference-between-MAX-and-MIN-tp7581058p7581062.html
> Sent from the RRDtool Users Mailinglist mailing list archive at Nabble.com.
>
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>

```