Index: firmware/App/Modes/ModeFill.c
===================================================================
diff -u -r22176ce95e49213c48454f34ddf5d29b8109f2cb -r669f36cf32c3b500aa2fd5b08c58ee5e6b2e7f08
--- firmware/App/Modes/ModeFill.c	(.../ModeFill.c)	(revision 22176ce95e49213c48454f34ddf5d29b8109f2cb)
+++ firmware/App/Modes/ModeFill.c	(.../ModeFill.c)	(revision 669f36cf32c3b500aa2fd5b08c58ee5e6b2e7f08)
@@ -69,6 +69,8 @@
 #define RO_PUMP_LOOKUP_TABLE_SIZE                       4                                                    ///< Size of array used as RO pump speed lookup table.
 #define CONCENTRATE_PUMP_PRIME_EXTRA_SPEED_ML_MIN       5.0F                                                 ///< Concentrate pump additional speed during priming in mL/min.
 #define CONCENTRATE_TEST_TIME_OUT_MS                    ( 30 * MS_PER_SECOND )                               ///< Concentrate test time out period in ms.
+// 2m long tubing to cap = 19.5 mL (acid line) + 7.92 mL/m * 2 m (tubing to cap) + 20.82 mL (straw) = 56.15 mL
+// Prime time in seconds = ( 56.15 mL / 48 mL/min ) x 60 second/min + 25 seconds margin time = 95 seconds.
 #define PRIME_CONCENTRATE_LINES_TIME_OUT_MS             ( 95 * MS_PER_SECOND )                               ///< Time required to prime the concentrate lines.
 #define FLUSH_BUBBLES_PUMP_TIME_OUT_MS                  ( 2  * MS_PER_SECOND )                               ///< RO pump on during flush bubble interval in ms.
 #define DIALYSATE_TEMPERATURE_TOLERANCE_C               2.0F                                                 ///< Dialysate temperature tolerance in degree C.