diff --git a/src/oceanic_veo250.c b/src/oceanic_veo250.c
index 58c0150..3288a5c 100644
--- a/src/oceanic_veo250.c
+++ b/src/oceanic_veo250.c
@@ -105,8 +105,6 @@ oceanic_veo250_send (oceanic_veo250_device_t *device, const unsigned char comman
 static device_status_t
 oceanic_veo250_transfer (oceanic_veo250_device_t *device, const unsigned char command[], unsigned int csize, unsigned char answer[], unsigned int asize)
 {
-	assert (asize == OCEANIC_VEO250_PACKET_SIZE + 2);
-
 	// Send the command to the device. If the device responds with an
 	// ACK byte, the command was received successfully and the answer
 	// (if any) follows after the ACK byte. If the device responds with
@@ -147,22 +145,14 @@ oceanic_veo250_transfer (oceanic_veo250_device_t *device, const unsigned char co
 	}
 
 	// Receive the answer of the dive computer.
-	int n = serial_read (device->port, answer, OCEANIC_VEO250_PACKET_SIZE + 2);
-	if (n != OCEANIC_VEO250_PACKET_SIZE + 2) {
+	int n = serial_read (device->port, answer, asize);
+	if (n != asize) {
 		WARNING ("Failed to receive the answer.");
 		return EXITCODE (n);
 	}
 
-	// Verify the checksum of the answer.
-	unsigned char crc = answer[OCEANIC_VEO250_PACKET_SIZE];
-	unsigned char ccrc = checksum_add_uint8 (answer, OCEANIC_VEO250_PACKET_SIZE, 0x00);
-	if (crc != ccrc) {
-		WARNING ("Unexpected answer CRC.");
-		return DEVICE_STATUS_PROTOCOL;
-	}
-
 	// Verify the last byte of the answer.
-	if (answer[OCEANIC_VEO250_PACKET_SIZE + 1] != NAK) {
+	if (answer[asize - 1] != NAK) {
 		WARNING ("Unexpected answer byte.");
 		return DEVICE_STATUS_PROTOCOL;
 	}
@@ -337,27 +327,17 @@ oceanic_veo250_device_keepalive (device_t *abstract)
 	if (! device_is_oceanic_veo250 (abstract))
 		return DEVICE_STATUS_TYPE_MISMATCH;
 
-	// Send the command to the dive computer.
+	unsigned char answer[2] = {0};
 	unsigned char command[4] = {0x91,
 		(device->last     ) & 0xFF, // low
 		(device->last >> 8) & 0xFF, // high
 		0x00};
-	device_status_t rc = oceanic_veo250_send (device, command, sizeof (command));
-	if (rc != DEVICE_STATUS_SUCCESS) {
-		WARNING ("Failed to send the command.");
+	device_status_t rc = oceanic_veo250_transfer (device, command, sizeof (command), answer, sizeof (answer));
+	if (rc != DEVICE_STATUS_SUCCESS)
 		return rc;
-	}
-
-	// Receive the answer of the dive computer.
-	unsigned char answer[3] = {0};
-	int n = serial_read (device->port, answer, sizeof (answer));
-	if (n != sizeof (answer)) {
-		WARNING ("Failed to receive the answer.");
-		return EXITCODE (n);
-	}
 
 	// Verify the answer.
-	if (answer[0] != ACK || answer[1] != NAK || answer[2] != NAK) {
+	if (answer[0] != NAK) {
 		WARNING ("Unexpected answer byte(s).");
 		return DEVICE_STATUS_PROTOCOL;
 	}
@@ -383,6 +363,14 @@ oceanic_veo250_device_version (device_t *abstract, unsigned char data[], unsigne
 	if (rc != DEVICE_STATUS_SUCCESS)
 		return rc;
 
+	// Verify the checksum of the answer.
+	unsigned char crc = answer[OCEANIC_VEO250_PACKET_SIZE];
+	unsigned char ccrc = checksum_add_uint8 (answer, OCEANIC_VEO250_PACKET_SIZE, 0x00);
+	if (crc != ccrc) {
+		WARNING ("Unexpected answer CRC.");
+		return DEVICE_STATUS_PROTOCOL;
+	}
+
 	memcpy (data, answer, OCEANIC_VEO250_PACKET_SIZE);
 
 #ifndef NDEBUG
@@ -423,10 +411,18 @@ oceanic_veo250_device_read (device_t *abstract, unsigned int address, unsigned c
 		if (rc != DEVICE_STATUS_SUCCESS)
 			return rc;
 
-		memcpy (data, answer, OCEANIC_VEO250_PACKET_SIZE);
-
 		device->last = number;
 
+		// Verify the checksum of the answer.
+		unsigned char crc = answer[OCEANIC_VEO250_PACKET_SIZE];
+		unsigned char ccrc = checksum_add_uint8 (answer, OCEANIC_VEO250_PACKET_SIZE, 0x00);
+		if (crc != ccrc) {
+			WARNING ("Unexpected answer CRC.");
+			return DEVICE_STATUS_PROTOCOL;
+		}
+
+		memcpy (data, answer, OCEANIC_VEO250_PACKET_SIZE);
+
 #ifndef NDEBUG
 		message ("VEO250Read(0x%04x,%d)=\"", address, OCEANIC_VEO250_PACKET_SIZE);
 		for (unsigned int i = 0; i < OCEANIC_VEO250_PACKET_SIZE; ++i) {
diff --git a/src/oceanic_vtpro.c b/src/oceanic_vtpro.c
index 095a284..4b14e36 100644
--- a/src/oceanic_vtpro.c
+++ b/src/oceanic_vtpro.c
@@ -40,6 +40,7 @@
 
 #define ACK 0x5A
 #define NAK 0xA5
+#define END 0x51
 
 typedef struct oceanic_vtpro_device_t {
 	oceanic_common_device_t base;
@@ -187,23 +188,14 @@ static device_status_t
 oceanic_vtpro_quit (oceanic_vtpro_device_t *device)
 {
 	// Send the command to the dive computer.
+	unsigned char answer[1] = {0};
 	unsigned char command[4] = {0x6A, 0x05, 0xA5, 0x00};
-	device_status_t rc = oceanic_vtpro_send (device, command, sizeof (command));
-	if (rc != DEVICE_STATUS_SUCCESS) {
-		WARNING ("Failed to send the command.");
+	device_status_t rc = oceanic_vtpro_transfer (device, command, sizeof (command), answer, sizeof (answer));
+	if (rc != DEVICE_STATUS_SUCCESS)
 		return rc;
-	}
 
-	// Receive the answer of the dive computer.
-	unsigned char answer[2] = {0};
-	int n = serial_read (device->port, answer, sizeof (answer));
-	if (n != sizeof (answer)) {
-		WARNING ("Failed to receive the answer.");
-		return EXITCODE (n);
-	}
-
-	// Verify the answer.
-	if (answer[0] != 0x5A || answer[1] != 0x51) {
+	// Verify the last byte of the answer.
+	if (answer[0] != END) {
 		WARNING ("Unexpected answer byte(s).");
 		return DEVICE_STATUS_PROTOCOL;
 	}
@@ -216,27 +208,18 @@ static device_status_t
 oceanic_vtpro_calibrate (oceanic_vtpro_device_t *device)
 {
 	// Send the command to the dive computer.
+	// The timeout is temporary increased, because the
+	// device needs approximately 6 seconds to respond.
+	unsigned char answer[2] = {0};
 	unsigned char command[2] = {0x18, 0x00};
-	device_status_t rc = oceanic_vtpro_send (device, command, sizeof (command));
-	if (rc != DEVICE_STATUS_SUCCESS) {
-		WARNING ("Failed to send the command.");
-		return rc;
-	}
-
-	// Receive the answer of the dive computer. The timeout
-	// is temporary increased, because the device needs
-	// approximately 6 seconds to respond.
-	unsigned char answer[3] = {0};
 	serial_set_timeout (device->port, 9000);
-	int n = serial_read (device->port, answer, sizeof (answer));
+	device_status_t rc = oceanic_vtpro_transfer (device, command, sizeof (command), answer, sizeof (answer));
 	serial_set_timeout (device->port, 3000);
-	if (n != sizeof (answer)) {
-		WARNING ("Failed to receive the answer.");
-		return EXITCODE (n);
-	}
+	if (rc != DEVICE_STATUS_SUCCESS)
+		return rc;
 
-	// Verify the answer.
-	if (answer[0] != ACK || answer[2] != 0x00) {
+	// Verify the last byte of the answer.
+	if (answer[1] != 0x00) {
 		WARNING ("Unexpected answer byte(s).");
 		return DEVICE_STATUS_PROTOCOL;
 	}
@@ -368,23 +351,14 @@ oceanic_vtpro_device_keepalive (device_t *abstract)
 		return DEVICE_STATUS_TYPE_MISMATCH;
 
 	// Send the command to the dive computer.
+	unsigned char answer[1] = {0};
 	unsigned char command[4] = {0x6A, 0x08, 0x00, 0x00};
-	device_status_t rc = oceanic_vtpro_send (device, command, sizeof (command));
-	if (rc != DEVICE_STATUS_SUCCESS) {
-		WARNING ("Failed to send the command.");
+	device_status_t rc = oceanic_vtpro_transfer (device, command, sizeof (command), answer, sizeof (answer));
+	if (rc != DEVICE_STATUS_SUCCESS)
 		return rc;
-	}
 
-	// Receive the answer of the dive computer.
-	unsigned char answer[2] = {0};
-	int n = serial_read (device->port, answer, sizeof (answer));
-	if (n != sizeof (answer)) {
-		WARNING ("Failed to receive the answer.");
-		return EXITCODE (n);
-	}
-
-	// Verify the answer.
-	if (answer[0] != ACK || answer[1] != 0x51) {
+	// Verify the last byte of the answer.
+	if (answer[0] != END) {
 		WARNING ("Unexpected answer byte(s).");
 		return DEVICE_STATUS_PROTOCOL;
 	}
@@ -446,7 +420,7 @@ oceanic_vtpro_device_version (device_t *abstract, unsigned char data[], unsigned
 		}
 
 		// Verify the last byte of the answer.
-		if (answer[OCEANIC_VTPRO_PACKET_SIZE / 2 + 1] != 0x51) {
+		if (answer[OCEANIC_VTPRO_PACKET_SIZE / 2 + 1] != END) {
 			WARNING ("Unexpected answer byte.");
 			return DEVICE_STATUS_PROTOCOL;
 		}