North is indicated when the two sets of pulses exactly coincide. South is indicated when pulses from one switch occur exactly midway between consecutive pulses from the other switch. The pressure sensor is a small solid state device. A quartz membrane over an evacuated chamber flexes as the pressure changes. Resistance elements on the membrane translate its flex into voltage levels that are converted to digital signals and sent to the microprocessor.
Readings are stable because each sensor is individually temperature compensated.
You can use the system from sea level to 15,000 feet without factory recalibration. Pressure changes are shown numerically - not with arrows. Pressure changes are determined over a full 3 hours. Pressure change data is updated every 10 minutes. The pressure change alarm can be set for increasing or decreasing pressure.