In 2^ minus ddCt method, why is the "minus" sign? - (Jan/24/2014 )

For the qPCR relative quantitation, we use the 2^-ddCt method. I was wondering why the minus sign before ddCt?

If I understood it correctly, ddCt is dCt(sample) - dCt(reference), -ddCt would be -(dCt(sample) - dCt(reference)), which equals dCt(reference) - dCt(sample), so it's just another way of calculating.

But I have also seen ddCt referred to as dCt(reference) - dCt(sample), then it would be the other way round...