DS checks that check multiple values in analysis.cfg

Hi, has anyone done DS checks in analysis.cfg that test multiple values
from the same rrd file?  We have data in ncv format that gets written to an
rrd file and I want to be able to check expressions against multiple values
at the same time, e.g. in logic, where A, B, C and D are all graphed in the
same rrd file :

If A + B / C > 33% go red
But if C < 10 go green anyway (override the above calculation, as it would
not be statistically reliable)
And if D > 30 go green anyway

The man page doesn't state how rules should be written:
http://xymon.sourceforge.net/xymon/help/manpages/man5/analysis.cfg.5.html#lbAN

I've tried to read the code:
https://sourceforge.net/p/xymon/code/HEAD/tree/branches/4.3.29/xymond/client_config.c
But I'm not a C programmer so that didn't help me.

Can anyone help?

Kind regards,

SebA