Yeah thats how I figured it. It knows you are 2.34567 nm from the missed approach point and AT 2.34567nm you need to be at 784 feet and that is how it determines the glide path information. But my question was how does it compute deviance? But lets say you are at 850 feet when you should be at 784, how does the GPS know your actual altitude and thus give you a deviance indication (fly down needle)?

LAAS will be cool when it starts to become implemented - am I correct that there is no civilian LAAS approaches in use publicly?