graph positive and negative values

["Matthew Tice" <mjtice (at) gmail.com>]

Hi, I'm wondering if anyone has been successful setting up and graphing an
item that fluctuates between positive and negative values?  I'm trying to
trend the temperature of my freezer.  When I created the rrd earlier today
(when positive values were generated) the graph was functional.  When I put
my sensors inside the freezer (where the temperatures drop a few degrees
below zero F) the values wouldn't drop below zero on the graph.
I tried modifying the current rrd tool with:
rrdtool tune /home/hobbit/data/rrd/tice/freezer.rrd --minimum freezerf:U
(which did drop the minimum to nan) but I still couldn't get negatives to
show on the graph.  I thought I'd delete the rrd and start over - but I
think now that the values are negative numbers the rrd won't even create.
 Here is a snippet from my hobbitgraph and hobbitserver files

[freezer]
       TITLE Freezer Temperature
       YAXIS Degrees
       DEF:tl=freezer.rrd:freezerf:AVERAGE
       #CDEF:wipeoutf=tl,-1,*
       DEF:cel=freezer.rrd:freezerc:AVERAGE
       #CDEF:wipeoutc=cel,-1,*
       LINE2:tl# (at) COLOR@:Temperature F
       #LINE2:wipeoutf# (at) COLOR@:Temperature -F
       LINE2:cel# (at) COLOR@:Temperature C
       #LINE2:wipeoutc# (at) COLOR@:Temperature -C
       COMMENT:\n
       GPRINT:tl:LAST:Temperature F\: %2.1lf (cur)
       GPRINT:tl:MAX:\: %2.1lf (max)
       GPRINT:tl:MIN:\: %2.1lf (min)
       GPRINT:tl:AVERAGE:\: %2.1lf (avg)\n
       GPRINT:cel:LAST:Temperature C\: %2.1lf (cur)
       GPRINT:cel:MAX:\: %2.1lf (max)
       GPRINT:cel:MIN:\: %2.1lf (min)
       GPRINT:cel:AVERAGE:\: %2.1lf (avg)\n


NCV_freezer="*:GAUGE"
(with freezer=ncv at the end of TEST2RRD and freezer and the end of GRAPHS).

Here is my script that generates the NCV for the rrd:

#!/bin/sh
COLUMN=freezer      # Name of the column
COLOR=green     # By default, everything is OK

[ -f ./.digitemprc ] || /usr/local/bin/digitemp_DS9097U -s/dev/ttyS0 -i

TEMPERATURE=$(/usr/local/bin/digitemp_DS9097U -s/dev/ttyS0 -a | awk '{print
$9}' | tail -1 | awk -F. '{print $1}')

if [ "${TEMPERATURE}" -gt 30 ]; then
COLOR=red
MSG="Temperature above 30 degrees"
else
COLOR=green
MSG="Temperature normal"
fi

# Section for data graphing
TEMPERATURE2_F=$(/usr/local/bin/digitemp_DS9097U -s/dev/ttyS0 -a | awk
'{print $9}' | tail -1)
TEMPERATURE2_C=$(/usr/local/bin/digitemp_DS9097U -s/dev/ttyS0 -a | awk
'{print $7}' | tail -1)

echo "freezerf : ${TEMPERATURE2_F}" > $BBTMP/freezer_f.txt
echo "freezerc : ${TEMPERATURE2_C}" > $BBTMP/freezer_c.txt
##


$BB $BBDISP "status $MACHINE.freezer $COLOR $MSG
`cat $BBTMP/freezer_f.txt`
`cat $BBTMP/freezer_c.txt`
"

rm $BBTMP/freezer_f.txt
rm $BBTMP/freezer_c.txt

exit 0


If anyone has an idea please let me know - I'd really like to trend this
data.

Thanks,

Matt