Lightning Pressure Head/Pitot Static Tube

As Bri pointed out in an earlier message, the pressure head received pitot and static pressure. Pitot pressure entered at the tip of the pressure head. Set back from the the tip was a ring of small holes which received static pressure. Static pressure gives an indication of height. Before take off the pilot sets the local barometric pressure for ground level at the airfield (QNH) or the equivalent of sea level (QFE), any changes in height are then referenced to one of these datums.
The pitot and static pressures in the Lightning fed into transducers and electrical signals then fed into the Air Data Computer. In the ADC, static voltage signal (S) gave barometric height, pitot minus static (P – S) gave Indicated Air Speed and P – S divided by S gave Mach Number.
The position of the pressure head was intended to minimise the effect of the build up of the shock wave, however the height readings could be affected, even more than indicated air speed. This was exacerbated by aircraft attitude, which could be affected by the stores carried (missiles, fuel tanks, etc).
This may not have mattered too much in a Lighting climbing to intercept a target. However the Buccaneer used an almost identical Air Data System. The altitude indication error induced by movement of the pressure wave and different combinations of stores could lead to a variation of hundreds of feet on the altimeter. With a low level aircraft, this sort of height error could lead to a very deep furrow.