Values below zero doesn't work

[Franky!]

Hi!

I have to monitor temperatures with an USB thermometer (I have to use a shell script that makes a "cat /dev/ttyUSB0") that gives me a value like this:
+018.3
That's working fine. But if the value is below zero like this:
-001.8
The graph didn't show me that values.

What can I do to make it work?

Thanks,
Frank

[gandalf]

First, change the MINIMUM value in the data template to sth. negative. Then, rrdtool tune --minimum all existing rrd files to get the data in.
Reinhard

[Franky!]

Ok thanks! Now I can see the actual -1.2 degrees celcius.
But directly after changing it I have had a really strage value: 508.1m degrees! That now the new maximum. What's wrong?

Frank

[gandalf]

508.1m is 0.5081 degrees (m = milli)
If you're worried, please post a screenshot
Reinhard