I'm trying to layout balusters on a porch railing and I can not remember the trick that Tom Silva demonstrated on Episode 506 I believe. He stretched a measuring tape the distance of the railing, and then pivoted the tape up to some degree / measurement and from there he marked off every 4 inches on the diagonal. Then he drew down 90 degrees to the horizontal line and that was his even spacing for the centers of the balusters.

Anyone know the details of this trick? How far did Tom pivot the tape? What were the steps he used to determine the spacing?