@@mikec1096 Because when doing fluild dynamics and Cp calculations, "pressure depends on the distance x from a reference line usually taken as the leading edge of the object"[1].. as a result, anyone who provides the Cp and Cg of a rocket, will always measure from the tip (where the pressure on the fusilage begins ot act)... unless your rocket flys backwards.. which will happen if you get them backwards. ;) Also.. likewise, Open Rocket does all of it's Cp/Gp figured from the tip. Lastly.. Cg (if measured) is only usable with a fully loaded rocket (motor + chute + wadding + electronics, etc). It's good to get a "dry" measurement just to see what Open Rocket thinks your dry weight and Cg are so you can "tune in" the model of your rocket, but once that's dialed in.. Your pre-flight RSO's safety check will always ask you what your loaded Cg & Cp measurements are (from the tip). If you measure the rear in front of them, they probably won't let you fly a HP rocket at their launch. ;) [1] - www.grc.nasa.gov/WWW/k-12/airplane/cp.html
As a general convention, yes ... these values are measured from the tip. But as long as you measure both CG and CP from the same point, it doesn't matter which end you measure from.
