BODC HEADED DOCUMENT NO. 27731 Applies to BODC Series Ref. Nos.: 33693, 33700, 33712, 33724, 33736, 33748, 33761, 33773, 33785, 33797, 33804, 33816, 33828, 33841, 33853, 33865, 33877, 33889, 33890, 33908, 33921, 33933, 33945, 33957, 33969, 33970, 33982, 33994, 34008, 34021, 34033, 34045, 34057, 34069, 34070, 34082, 34094, 34101, 34113, 34125, 34137, 34149, 34174, 34186, 34198, 34205, 34217, 34229, 34230, 34242, 34254, 34266, 34278, 34291, 34309, 34310, 34322, 34334 I.O.S. Calibration and Data Processing of Off-Shore Tide Gauge Data Calibration of pressure/frequency sensors and thermistors are carried out using the facilities and staff at I.O.S. Bidston with the exception of pre 1975 pressure/frequency sensors, which were calibrated in the pressure chamber at I.O.S. Wormley. The data are copied from the logger magnetic tape to 9 track magnetic tape and disk. The data are either listed or plotted as an initial check. A program is then used to check the data from the temperature sensor channels, calculate and plot the temperature values and store them (if temperature sensor channels are available). A second program performs a similar function for the pressure sensor channel, using the pressure frequency coefficient to convert each pressure frequency to the frequency at the reference temperature and calculating the pressures using the pressure frequency calibration. The data values, generally at 15 minute intervals, but occasionally at 10 minute intervals, of pressure are then plotted and stored. If waterhead is required, it may be computed by subtracting atmospheric pressure and applying the hydrostatic relation:- H = P / ( d * g ) H = waterhead (cm) P = pressure (0.01 mb) d = density (kg/m3) g = gravitational acceleration (m/s2)