Isa deviation

Hello all.  

I have a question about Isa deviation and I can not work it out. 

the details are 12000 feet and 0c. 

15-24 gives an Isa temp of -9 but the deviation is 9. 

the problem I have is I would have thought this is -9 and don’t understand why it is a positive not a negative.  

if anybody can show me what I am doing wrong would be great. 

The temp should be -9, because it is warmer than standard at 0 the deviation is +9

The temp should be -9, because it is warmer than standard at 0 the deviation is +9

 

Thanks.  I think it just clicked.  The deviation is +9 to get from -9 back to 0.  

so for 2000 feet and 2c you would end up as -9 because you have to get from 11 back to 2.  

is that correct?

Jonkers, don't stress just goen have a fly and enjoy it.