dbcheck, custom graphs and strange results

[Gildas Le Nadan <gn1 (at) sanger.ac.uk>]

Hello,

I am trying to graph the value of the "Opens" value produced by dbcheck 
when monitoring mysql.

I defined the value as DERIVE in NCV_mysql instead of GAUGE, as this is 
a value that is growing while the mysql instance is running (if the 
mysql instance restart it restarts from 0).

For instance, I have the following:

time  | Opens | diff | graph'd | diff/graph'd
      | value | t'-t | value   | value
------+-------+------+---------+-------------
10:14 | 22732 |  -   |  -      |   -
10:19 | 22765 | +33  | 110m    | 3.33
10:24 | 22806 | +41  | 128m    | 3.12
10:29 | 22821 | +15  | 50m     | 3.33
10:34 | 22835 | +14  | 48m     | 3.2

I was expecting the graphed value to be equal to the diff value, but the 
units are wrong (m instead of unit), and the value is wrong as well 
(with a somewhat constant 3.xx ratio).

Any idea where this comes from? (I suspect this is me being stupid and 
not understanding some of the underlying rrd subtleties)

Cheers,
Gildas