A consideration of the factors suggesting that new types of flying instruments are becoming necessary.

To safeguard the aircraft and crew against the danger of excessive speed and normal acceleration loads, until recently it was considered sufficient to provide for the pilot an airspeed indicator and to fix in the aircraft a plate giving the maximum safe speeds permitted for diving, without and with external stores, flaps and undercarriage down and so on. In the case of Service aircraft these limitations are usually published in Pilot's Notes for the type. Based on design data these speeds are those at which, allowing suitable factors of safety, the stresses in the appropriate parts of the aircraft's structure are calculated to reach the maximum safe limits.