176 mph reading is possible, since the 428 Nelsons tend to unload to about 22K in the air. Also most people don't notice a 5 mph breeze, and even a slight dive will add 3-5 in the trap. But in race trim pulling Gee's very few will crack 170.

On the other hand, parrallax error will result in a slower than true speed. If you are standing just 7 degrees off axis from the path of flight, you have a 1% error.