diff --git a/24c16.c b/24c16.c
index 8f07d40..cba3e62 100644
--- a/24c16.c
+++ b/24c16.c
@@ -19,7 +19,7 @@ int update_checksum(t_eeprom_data* data)
 
 	p_data = (char*)data;
 
-	for (size_t i=0; i<sizeof(*data); i++)
+	for (size_t i=0; i < (sizeof(*data) - sizeof(data->checksum)); i++)
 	{
 		checksum += *p_data;
 		p_data++;
@@ -27,6 +27,7 @@ int update_checksum(t_eeprom_data* data)
 
 	//fprintf(stderr, "Checksum: %x\n", checksum);
 	data->checksum = checksum;
+
 	return (0);
 }
 
@@ -56,7 +57,7 @@ char verify_checksum(t_eeprom_data* data)
 
 	p_data = (char*)data;
 
-	for (size_t i=0; i<sizeof(*data); i++)
+	for (size_t i=0; i < (sizeof(*data) - sizeof(data->checksum)); i++)
 	{
 		checksum += *p_data;
 		p_data++;
diff --git a/24c16.h b/24c16.h
index b47e8fe..3cca5d7 100644
--- a/24c16.h
+++ b/24c16.h
@@ -2,6 +2,8 @@
 
 #define EEPROM_DATA_VERSION 1
 
+#define SN_LENGTH 8
+
 // define struct for MS5611 sensor
 typedef struct {
 	int fd;
@@ -11,11 +13,14 @@ typedef struct {
 typedef struct {
 	char header[3];
 	char data_version;
-	char serial[6];
 	float zero_offset;
+	char serial[SN_LENGTH];
+	char padding[3];
 	char checksum;
 } t_eeprom_data;
 
+
+
 // prototypes
 int eeprom_open(t_24c16 *, unsigned char);
 char eeprom_write(t_24c16 *, char *, unsigned char, unsigned char);
diff --git a/sensorcal.c b/sensorcal.c
index 132887a..e5aa415 100644
--- a/sensorcal.c
+++ b/sensorcal.c
@@ -83,7 +83,7 @@ int main (int argc, char **argv) {
 	int result;
 	int c;
 	int i;
-	char sn[7];
+	char sn[SN_LENGTH];
 	char zero[1]={0x00};
 
 
@@ -128,8 +128,9 @@ int main (int argc, char **argv) {
 				}
 				strcpy(data.header, "OV");
 				data.data_version = EEPROM_DATA_VERSION;
-				memset(data.serial,'0',6);
+				memset(data.serial,'0',SN_LENGTH);
 				data.zero_offset=0.0;
+				memset(data.padding,'0',3);
 				update_checksum(&data);
 				printf("Writing data to EEPROM ...\n");
 				result = eeprom_write(&eeprom, (char*)&data, 0x00, sizeof(data));
@@ -171,7 +172,7 @@ int main (int argc, char **argv) {
 				printf("Reading EEPROM values ...\n\n");
 				if( eeprom_read_data(&eeprom, &data) == 0)
 				{
-				  memcpy(sn,data.serial,6);
+				  memcpy(sn,data.serial,SN_LENGTH);
 					printf("Actual EEPROM values:\n");
 					printf("---------------------\n");
 					printf("Serial: \t\t\t%s\n", sn);
@@ -189,12 +190,12 @@ int main (int argc, char **argv) {
 				break;
 
 			case 's':
-				if( strlen(optarg) == 6)
+				if( strlen(optarg) == SN_LENGTH)
 				{
 					// read actual EEPROM values
 					if( eeprom_read_data(&eeprom, &data) == 0)
 					{
-						for(i=0; i<6;i++)
+						for(i=0; i<SN_LENGTH;i++)
 						{
 							sn[i]=data.serial[i]=*optarg;
 							optarg++;
@@ -214,7 +215,7 @@ int main (int argc, char **argv) {
 				}
 				else
 				{
-					printf("ERROR: Serialnumber has to have exactly 6 characters !!\n");
+					printf("ERROR: Serialnumber has to have exactly 8 characters !!\n");
 					exit_code=1;
 					break;
 				}