Need help with multiple RRD data points in one check

You can also make the graphs by hand.  Something like this should give you a PNG file you can load in your browser.  Tweak the graph settings until it looks right, then update the graphs.cfg for Xymon.

NOW=`date +%s`
START=`expr $NOW - 604800 - 604800`   # this sets the start to NOW-14 days
UPDATE=`date +'%F %T' | sed -e 's/:/\\\:/g'`
RRD=/var/lib/xymon/rrd/somehostname/something.rrd

rrdtool graph /var/www/html/somehostname.png \
    "DEF:thing=$RRD:thingvariable:AVERAGE" \
    "LINE2:thing#$COLOR:Total Thing Status" \
    "GPRINT:thing:LAST:\: %5.1lf %s (cur)" \
    "GPRINT:thing:MAX: %5.1lf %s (max)" \
    "GPRINT:thing:MIN: %5.1lf %s (min)"  \
    "GPRINT:thing:AVERAGE: %5.1lf %s (avg)\n" \
    "COMMENT:  Updated\: $UPDATE\n" \
    --title "Thing Status - 14 days" \
    --vertical-label "Thing"  \
    --width 864 \
    --height 120 \
    --start $START \
    --end $NOW