Phil White wrote: >To cut a very long story short, I am now of the opinion that I >should not set up my RRD store as > DS:$sensor:GAUGE:300:-50:100 > simply because this is not the information that I am *really* >interested in - it is just the way that most people do it, because >that is the way we are used to thinking. > >I'll try to explain a bit better. I have several sensors - some >inside the house, some outside. When I started, the aim was to >monitor the temperature, and use this to automate heating. But, >rather than the *actual* temperature, I am actually more interested >in the *relative* temperature difference between the average outside >temperature, and inside - together with the rate of change in >temperature (which are probably related in some way).
I think you'll find that avg(a)-avg(b) = avg(a-b) But if you did want to store difference, then keep the gauge data type, and store a-b - you'll probably want to store a or b as well if you want to see what the actual temperatures were. Where it gets more interesting is if you are interested in other derived values - eg min or max. Here, max (a-b) is not the same as max(a)-max(b), so you must store a-b (and it's derivatives) if you want to see/use such data. -- Simon Hobson Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed author Gladys Hobson. Novels - poetry - short stories - ideal as Christmas stocking fillers. Some available as e-books. _______________________________________________ rrd-users mailing list [email protected] https://lists.oetiker.ch/cgi-bin/listinfo/rrd-users
