greater accuracy than the conventional method, particularly where vari~able and irregulayyloading is involved, e.g., the center of pressure on the wing displaced toward the trailing edge. The purpose of any calibration is the establishment of a rela- tionship cetween instrumentation output and the magnitude of the function being mezsured. Experimental calibration is sometimes approximate because of the difficulty in simulating ectual inputs of a known, control= lable value, as for example in the calibration of a pressure transducer. Reliability of many experimental calibrations, therefore, must be determined, in part, from theoretical considerations. The procedures used in calibrating the instrumentation installed in the B+36 and Be47 aircraft were primilary the same 4s those used in past operations. These procedures are described in detail in Chapters 2 and 3 of Greenhouse Report wT-31.” 2.3.7.1 ##Pressure and acceleration As mentioned previously in paragraph 2.3.1.1, both the Wiancko pressure gage and the Cook High Frequency Pressure Recorder were used for overpressure measurements. The former gage utilized a torsional diaphrazm-veriable reluctance transducer, whereas the latter gage employ=ed a crystal microphone as the pressure sensing element. The output of coth gages was amplified prior to recording; however, the émplifier ¢for the crystal microrhone did not respond to frequencies below 20 cps. Thus, the Cook system could not measure static pressure levels as could the Wiancnxo gece. For cezlitration, the wianko gage was hooked-up as it was for actual operation and the circuit balanced for zero galvanometer deflection. Using the calibrate steps provided in the bridge arplifier, a positive and negative calibration step was introduced into the circvit and the resulting galvanometer defiections measured. The gage was then subjected to various positive and negative pressures of known value to determine galvanometer deflection as a function of pressure. The deflections were read as percentages of the deflection obtained for the calibrate step and were recorded as percentages of cal-plus (positive calibration step) or cal-minus (negative calicration step). The galvanometer deflection ottained in the calibration step is defined as 100 per cent cal. The resulting calicration curve for the gage is a rlot of pressure versus per cent of a known calivrating signal (per cent cal). The calig bration curve was drawn as a straight line. If the data points were found to deviate significantly from a straight lire after repeated cali- brations, the gage was not used. Theoretically, a linear response should be obtained. after the static pressure calitration, the gage was rechecked in a shock tube. The Cook High Freauency Pressure Recorder contains a calibration circuit that produces a 0.62V 400 cycle square wave output whith is equivalent in voltage level to the output of the crystal when subjected to a blast pressure of 2 psi. This signal is introduced into the system at the pressure transducer and follows the same path as the tra:..ducer signal to produce ultim:tely a trace on the photo-rarphic record, The maximum displacement of tne trace represents the displacement thet will be cbtained for a 2 psi inrut if the system is orerating properly. Over-all AL