[rrd-users] rate of change

[Alan Jurgensen]

I want to calculate the rate of change percentage, and add that as a
comment/gprint at bottom of graph.

assumption:  ROC = (y1 - y0) / (x1 - x0) 

my rrd is a gauge of disk space used in bytes.
i assume all I need is to keep the first byte value (y0)
and first timestamp (x0), then cdef it like this:

CDEF:roc=y1,y0,-,TIME,x0-,/

but howto save first values (time = x0, bytes = y0)?
this doesnt work:

CDEF:y0=y0,UN,used,y0,IF
CDEF:x0=x0,UN,TIME,x0,IF

Howto save first values?
any other suggestions for ROC calculation?

thx, JurgyMan


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