Woodpecker usually seems to think out their tools pretty thoroughly but I think they missed the boat on this one. Because of the offset between the two bars, it would be easy to measure on the diagonal rather than parallel to the rods. Think about measuring between the bottom of the grooves for a drawer bottom, the tool has to be tilted so that the tips go into opposite grooves - if you don't measure across the tips at the same angle, the measurement will be slightly out. The solution for this would be a link that attaches to the end of one rod; the link would have two holes in it, spaced the same as the rods - one end attaches to the rod and the lower one accepts the tip. I have one of the Lee Valley Bar Gauges - I glued a short piece of wood under the one end so that the tip was in line with the other end so can eyeball that both ends are about the same distance down from a reference face and I know it's not tilted.