or Proof Pressure is the maximum pressure that can be applied to a pressure instrument without significantly effecting its reading accuracy. Some manufacturers will state a maximum calibration shift following an over-pressure condition where others will state that the specification is unaffected.
Found on http://www.sensorsone.co.uk/pressure-measurement-glossary.html
Overpressure (or blast overpressure) is the pressure caused by a shock wave over and above normal atmospheric pressure. The shock wave may be caused by sonic boom or by explosion, and the resulting overpressure receives particular attention when measuring the effects of nuclear weapons or thermobaric bombs. == Effects of overpressure == According ... Found on http://en.wikipedia.org/wiki/Overpressure