Calculate Difference between MAX and MIN

[utopiazz]

I have been fooling around with Cacti for som time and it works fine on my serer. What i do is collecting temperature readings from Dallas/Maxim-IC temperature and counter probes on my heatingsystem.

The only thing i havent found out yet (so far) is how to print the difference between the maximum and minimum values on a graph.

The collected data is counter readings and i want to display a GPRINT with the difference between the starting and ending points on my graph.

http://www.mysite.se/cacti/graph.php?ac ... view_type=

I't should be very simple but i fail to complete this task

/Johan

[utopiazz]

Was the question to hard to understand or is it not supported to do this kind of calculation with GPRINT. Is it possible to do it some other way im more than willing to try

/Johan

[gandalf]

To be honest: I did understand, but I do not know the way to solve.
But here's a workaround:
What about defining the reading not as a GAUGE but as a COUNTER? This will result in a graph showing the increase from interval to interval (see rrdtool docs at http://www.rrdtool.org for a more decent understanding). Then you'll use the Total function described in the later chapters of cacti doc (see Bandwidth Summation at http://www.cacti.net/downloads/docs/html/variables.html)
Reinhard

[utopiazz]

I have collected the same data as both GAUGE and COUNTER so it would be a pretty easy task to try this since i have all data both ways.

Reagards

/Johan

[utopiazz]

Well, the TOTAL was pretty easy to test but it didn't solve my issue.

The data i have is collected from a MaximIC pulse counter. The data is collected every 2minutes.
Every pulse i count represent 5 liters of water. To present that on the graph in cubic meters i have a CDEF that transforms the COUNT value to m3.

And since the SUM funktion can't use any CDEF i only get the total number of pulses counted over the period and not cubic meters.

/Johan