dateTime = PressureData.DATETIME;
pressure = PressureData.Pressure;
plot(dateTime, pressure)
figure
plot(pressure)
excelDateTime = exceltime(dateTime);
seconds = (excelDateTime - excelDateTime(1)) * 24.0 * 3600.0;

P1 = polyfit(seconds(400:475), pressure(400:475), 1);
P2 = polyfit(seconds(507:572), pressure(507:572), 1);