Index: firmware/App/Controllers/Pressures.c
===================================================================
diff -u -r00c9d70ee1398f0c6db39a011220f830db92cfd3 -r0c3720e7797f056a490cf8dd1880e34ac5ede37c
--- firmware/App/Controllers/Pressures.c	(.../Pressures.c)	(revision 00c9d70ee1398f0c6db39a011220f830db92cfd3)
+++ firmware/App/Controllers/Pressures.c	(.../Pressures.c)	(revision 0c3720e7797f056a490cf8dd1880e34ac5ede37c)
@@ -35,7 +35,8 @@
 #define PRESSURES_DATA_PUB_INTERVAL         ( MS_PER_SECOND / TASK_PRIORITY_INTERVAL )  ///< interval (ms/task time) at which the pressures data is published on the CAN bus.
 
 #define PUMP_PRESSURE_ZERO                  0x309        ///< ADC counts equivalent to 0 PSI for pump in/out pressure sensors.
-#define PUMP_PRESSURE_PSI_PER_COUNT         0.06343      ///< PSI per ADC count conversion factor for pump in/out pressure sensors.
+#define PUMP_PRESSURE_PSIA_PER_COUNT        0.06343      ///< PSIA per ADC count conversion factor for pump in/out pressure sensors.
+#define PUMP_PRESSURE_PSIA_TO_PSI_OFFSET    14.7         ///< Subtract this offset to convert PSIA to PSI.
 
 /// Defined states for the pressures monitor state machine.
 typedef enum PresOccl_States
@@ -158,10 +159,10 @@
     S32 drainOut = (S32)getIntADCReading( INT_ADC_DRAIN_PUMP_INLET_PRESSURE );
 
     // convert ADC counts to PSI for each sensor
-    pressures[ PRESSURE_SENSOR_RO_PUMP_INLET ].data = (F32)( roIn - PUMP_PRESSURE_ZERO ) * PUMP_PRESSURE_PSI_PER_COUNT;
-    pressures[ PRESSURE_SENSOR_RO_PUMP_OUTLET ].data = (F32)( roOut - PUMP_PRESSURE_ZERO ) * PUMP_PRESSURE_PSI_PER_COUNT;
-    pressures[ PRESSURE_SENSOR_DRAIN_PUMP_INLET ].data = (F32)( drainIn - PUMP_PRESSURE_ZERO ) * PUMP_PRESSURE_PSI_PER_COUNT;
-    pressures[ PRESSURE_SENSOR_DRAIN_PUMP_OUTLET ].data = (F32)( drainOut - PUMP_PRESSURE_ZERO ) * PUMP_PRESSURE_PSI_PER_COUNT;
+    pressures[ PRESSURE_SENSOR_RO_PUMP_INLET ].data = (F32)( roIn - PUMP_PRESSURE_ZERO ) * PUMP_PRESSURE_PSIA_PER_COUNT - PUMP_PRESSURE_PSIA_TO_PSI_OFFSET;
+    pressures[ PRESSURE_SENSOR_RO_PUMP_OUTLET ].data = (F32)( roOut - PUMP_PRESSURE_ZERO ) * PUMP_PRESSURE_PSIA_PER_COUNT - PUMP_PRESSURE_PSIA_TO_PSI_OFFSET;
+    pressures[ PRESSURE_SENSOR_DRAIN_PUMP_INLET ].data = (F32)( drainIn - PUMP_PRESSURE_ZERO ) * PUMP_PRESSURE_PSIA_PER_COUNT - PUMP_PRESSURE_PSIA_TO_PSI_OFFSET;
+    pressures[ PRESSURE_SENSOR_DRAIN_PUMP_OUTLET ].data = (F32)( drainOut - PUMP_PRESSURE_ZERO ) * PUMP_PRESSURE_PSIA_PER_COUNT - PUMP_PRESSURE_PSIA_TO_PSI_OFFSET;
 
     // TODO - any filtering required???