[rrd-users] Standard Deviation

[Berry Kercheval]

Hi.  I'm trying to figure out how to graph a value and its standard
deviation.  I searched the docs, tutorials and mailing list archives and
found a number of posts about *calculating* the std. dev. with CDEFs,
but in my case I already have values for the std dev.  The device I'm
monitoring aggregates the average time for certain operations *AND*
calculates the std dev for each time period's batch of operations.

So I'd like to graph the average value with "error bars" of one std dev
above and below.  The best I've been able to come up with is to do a
stacked graph of values with the background color from 0 to (avg -
stddev), one color from (avg - stddev) to (avg), a dot at avg of a
contrasting color, and then the first color from avg to (avg + stddev),
but this seems tedious and kludgy. 

My question, then, is "is there some sort of error bar/tolerance/stddev
graphing built in that I've missed in the docs and mailing list
archive?"