diff --git a/gpio/gpio.c b/gpio/gpio.c
index 3fc97a3..447e53d 100644
--- a/gpio/gpio.c
+++ b/gpio/gpio.c
@@ -66,23 +66,27 @@ int wpMode ;
 char *usage = "Usage: gpio -v\n"
               "       gpio -h\n"
               "       gpio [-g|-1] ...\n"
+              "         where -g: pin numbering according to readall BCM column\n"
+              "         where -1: pin numbering according to readall Physical column\n"
+              "         when omitted: pin numbering according to readall wPi column\n"
               "       gpio [-d] ...\n"
               "       [-x extension:params] [[ -x ...]] ...\n"
               "       gpio [-p] <read/write/wb> ...\n"
               "       gpio <mode/read/write/aread/awritewb/pwm/pwmTone/clock> ...\n"
               "       gpio <toggle/blink> <pin>\n"
-	      "       gpio readall\n"
-	      "       gpio wfi <pin> <mode>\n"
-	      "       gpio drive <group> <value>\n"
-	      "       gpio pwm-bal/pwm-ms \n"
-	      "       gpio pwmr <range> \n"
-	      "       gpio pwmc <divider> \n"
-	      "       gpio i2cd/i2cdetect\n"
-	      "       gpio rbx/rbd\n"
-	      "       gpio wb <value>\n"
-	      "       gpio usbp high/low\n"
-	      "       gpio gbr <channel>\n"
-	      "       gpio gbw <channel> <value>" ;	// No trailing newline needed here.
+              "       gpio readall\n"
+              "       gpio wfi <pin> <mode>\n"
+              "         where <mode> can be: rising, falling, both\n"
+              "       gpio drive <group> <value>\n"
+              "       gpio pwm-bal/pwm-ms \n"
+              "       gpio pwmr <range> \n"
+              "       gpio pwmc <divider> \n"
+              "       gpio i2cd/i2cdetect\n"
+              "       gpio rbx/rbd\n"
+              "       gpio wb <value>\n"
+              "       gpio usbp high/low\n"
+              "       gpio gbr <channel>\n"
+              "       gpio gbw <channel> <value>" ;	// No trailing newline needed here.
 
 
 #ifdef	NOT_FOR_NOW