Example of rrdtool GAUGE to store a value between 0 and 100

rrdgauge.sh

#!/bin/sh
rrdtool create foo.rrd --start -2h --step 900 DS:foo:GAUGE:3600:0:100 RRA:AVERAGE:0.5:1:1000
for N in $(seq 20 -1 1)
do
	rrdtool update foo.rrd -- -$(($N*600)):$N$N
	rrdtool lastupdate foo.rrd 
done
rrdtool graph --start -1h foo.png DEF:foo=foo.rrd:foo:AVERAGE LINE:foo#000000:thefoo
rrdtool fetch foo.rrd AVERAGE | tail