Yes I am aware some (many) schools teach it that way. But the FAA says use airspeed, which is more ideal for teaching purposes. Using ground speed in the equation is theoretically correct but it fosters confusion about how to do the maneuver. This thread is proof of that. Students get confused about how to calculate pivotal height. It is a one-tme calculation based on airspeed OR ground speed in no-wind conditions. You are looking at an airspeed dial in the airplane so it is best to use that. Ground speed is the cause of variation in pivotal altitude, so it certainly works to use it to compute the no-wind pivotal altitude. I am trying to make the distinction between the theory of pivotal altitude and the application of the pivotal altitude formula for pilots but it looks like I am missing my audience a bit. Refer to FAA 8083 Airplane Flying Handbook if you need to. It has the info needed to do the maneuver properly, even though the theory is mostly left out.