In the ASHRAE fitting database, there are negative duct fitting coefficients. I assume this means that that particular fitting will produce a pressure regain. However, I am unsure that it would be a static regain because: the formula is P(total)=C*P(velocity), and P(total) only can only drop as it travels thru a duct (downstream of the fan). Is this a contradition? So I am confused of what the negative means because of this contradiction. Anybody know?