kg4wsv:
That does not mean it is actually happening at a true 750ft.
So what will give you a "true" 750'?
Nothing that's easy to implement... 
Theoretically, if your rocket could accurately track two points of with a known and fixed distance apart (e.g. the launch pad and another point 50 feet away at roughly the same elevation) you could use triangulation to find an accurate distance. While the math is well within the capabilities of an Arduino, implementing an adequate tracking system would be much easier said than done, as well as add a non-trival amount of weight and volume.