Today, as far as I can see the gradient published in tab data is the one at 400 ft AGL
The newer electronic AFM's show the start and end gradients for the 2nd segment, they only comply with the FAR's at the start.
we do know that there are people "out there" who go flying with WAT as the only limit regardless of Runway / Obstacle computations
in the corporate world, this appears to be the norm.
The Gulf when climbing into an inversion after T/O
We actually use the inversion temperature for the whole takeoff calculation. We are probably considered extremely conservative, but considering we used to have 747's DESCENDING after takeoff with all engines running, the new procedure is worth the weight loss.
Mutt