a new problem with Ref()

["Guy Tann" <grt@xxxxxxxxxxxx>]

List,

Well I've programmed my way around the last problem, but I just hit another
snag.

Is there a limit in using the Ref() function?

I have a variable called MXX.  I am manipulating it in a simplistic manner
and the first 8 worked great.  When I get to the ninth iteration, it quits
working.

XEIGHT:=  ( MXX - Ref( MXX , -8 ) ) / 8;   This one works correctly
XNINE:= ( MXX - Ref( MXX , -9 ) ) / 9;       This one doesn't work!

Actually, numbers one through eight work fine.  Nine and ten don't work and
I haven't finished checking eleven through twenty yet.  I assume there's
something in the manual I missed, so any help would be appreciated.

Thanks,

Guy

" When I die, I want to go peacefully like my grandfather did, in his sleep.
Not yelling and screaming like the passengers in his car."