asterisk users - Oct 2008 - Problem in extensions.conf Configuration ${CALLINGPRES}

Dear Everybody,

I have to store variable from ${CALLINGPRES} and get birth date  of  our 
client and get back to him his birth prediction as numerology 
(numerology digit value is between 1-9). I have also mentioned below 
example here suppose client's birth date is 27-01-2000 then 
2+7+0+1+2+0+0+0 = 12 and then 1+2 = 3. 3 is result so client can get his 
prediction as this 3 digit.

Please guide me how can I write in extensions.conf

exten => 1,1,SetGlobalVar(A=${CALLINGPRES})
exten => 1,n,NoOp(${A})

How can I store variable from ${CALLINGPRES}. I have also tried 
SetVar(A=${CALLINGPRES}) instead of SetGlobleVar() but I have not get 
any integer variable.

-- 
With Regards,
Hiren Mistry