The top left speed indicator of vehicles do not take all X, Y and Z motion into account.
The speed indicator is an excellent measurement of a number of things:
- Motion
- Distance timing
- Impact damage
- Collision danger
- Helicopter landing aid
In helicopters, these can be applied not only to forward/backward motion, but also perpendicular side to side motion, with benefit.
OK if ascension / descension is not counted as it is displayed in realtime through the separate altitude meter, and would only confuse the pilot. But side to side motion does not count, only forward/backward motion, and in helicopters this does not make any sense.