diff --git a/include/libdivecomputer/parser.h b/include/libdivecomputer/parser.h
index f1f73bd..774e5e3 100644
--- a/include/libdivecomputer/parser.h
+++ b/include/libdivecomputer/parser.h
@@ -149,13 +149,36 @@ typedef enum dc_tankvolume_t {
     DC_TANKVOLUME_IMPERIAL,
 } dc_tankvolume_t;
 
+/*
+ * Tank volume
+ *
+ * There are two different ways to specify the volume of a tank. In the
+ * metric system, the tank volume is specified as the water capacity,
+ * while in the imperial system the tank volume is specified as the air
+ * capacity at the surface (1 ATM) when the tank is filled at its
+ * working pressure. Libdivecomputer will always convert the tank volume
+ * to the metric representation, and indicate the original tank type:
+ *
+ * DC_TANKVOLUME_NONE: Tank volume is not available. Both the volume and
+ * workpressure will be zero.
+ *
+ * DC_TANKVOLUME_METRIC: A metric tank. The workpressure is optional and
+ * may be zero.
+ *
+ * DC_TANKVOLUME_IMPERIAL: An imperial tank. Both the volume and
+ * workpressure are mandatory and always non-zero. The volume has been
+ * converted from air capacity to water capacity. To calculate the
+ * original air capacity again, multiply with the workpressure and
+ * divide by 1 ATM (Vair = Vwater * Pwork / Patm).
+ */
+
 typedef struct dc_tank_t {
-    unsigned int gasmix; /* Index of the gas mix, or DC_GASMIX_UNKNOWN */
-    dc_tankvolume_t type;
-    double volume; /* Wet or air volume (depending on the type) in liter */
-    double workpressure; /* Pressure in bar */
-    double beginpressure;
-    double endpressure;
+    unsigned int gasmix;  /* Gas mix index, or DC_GASMIX_UNKNOWN */
+    dc_tankvolume_t type; /* Tank type */
+    double volume;        /* Volume (liter) */
+    double workpressure;  /* Work pressure (bar) */
+    double beginpressure; /* Begin pressure (bar) */
+    double endpressure;   /* End pressure (bar) */
 } dc_tank_t;
 
 typedef union dc_sample_value_t {
diff --git a/src/atomics_cobalt_parser.c b/src/atomics_cobalt_parser.c
index 7a53746..83bcfc7 100644
--- a/src/atomics_cobalt_parser.c
+++ b/src/atomics_cobalt_parser.c
@@ -158,6 +158,8 @@ atomics_cobalt_parser_get_field (dc_parser_t *abstract, dc_field_type_t type, un
 	else
 		atmospheric = array_uint16_le (p + 0x26) * BAR / 1000.0;
 
+	unsigned int workpressure = 0;
+
 	if (value) {
 		switch (type) {
 		case DC_FIELD_DIVETIME:
@@ -183,9 +185,13 @@ atomics_cobalt_parser_get_field (dc_parser_t *abstract, dc_field_type_t type, un
 			switch (p[2]) {
 			case 1: // Cuft at psi
 			case 2: // Cuft at bar
+				workpressure = array_uint16_le(p + 10);
+				if (workpressure == 0)
+					return DC_STATUS_DATAFORMAT;
 				tank->type = DC_TANKVOLUME_IMPERIAL;
 				tank->volume = array_uint16_le(p + 8) * CUFT * 1000.0;
-				tank->workpressure = array_uint16_le(p + 10) * PSI / BAR;
+				tank->volume /= workpressure * PSI / ATM;
+				tank->workpressure = workpressure * PSI / BAR;
 				break;
 			case 3: // Wet volume in 1/10 liter
 				tank->type = DC_TANKVOLUME_METRIC;