[rrd-users] PREV

[LYLIX.NET Info]

I'm attempting to calculate the derivative of two adjacent points in the 
dataset during the graphing stage (yes, im aware the dataset can be 
created w/ the information already via DERIVE).  Here is what I've tried:

recvb -> cumulative amount of data transferred (bytes)
30 -> interval, though if it is possible to grab the previous time value 
and do an actual time delta calculation w/ the current datapoint's time, 
that would be best

CDEF:recvd=recvb,PREV(recvb),-,30,/
AREA:recvd#FF0000:"RX MBps\n"

Problem w/ that above is I get an error from BASH:

line 13: syntax error near unexpected token `('
line 13: ` CDEF:recvd=recvb,PREV(recvb),-,30,/ \'

So, how is one supposed to ever use the PREV() function if BASH is gg to 
complain of it?

- Eric

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