diff --git a/src/TimezonesGMT.h b/src/TimezonesGMT.h
index 4a51e32..1493dea 100644
--- a/src/TimezonesGMT.h
+++ b/src/TimezonesGMT.h
@@ -1,6 +1,7 @@
 #ifndef TIMEZONES_GMT_H
 #define TIMEZONES_GMT_H
 
+// This file is used to set up GMT based timezones.
 
 // You don't need to change anything here to be able to set up GMT based time.
 // If you set TIMEZONES_NON_GMT_OVERRIDE to 1 (as for get summer time and leaps),
@@ -10,11 +11,14 @@
 // Visit the link below.
 
 #ifndef TIMEZONES_NON_GMT_OVERRIDE
-#define TIMEZONES_NON_GMT_OVERRIDE 0
+#define TIMEZONES_NON_GMT_OVERRIDE 0 // 0: GMT, 1: Location timezone.
 #endif
 
+#ifndef TIMEZONES_SELECTED
+#define TIMEZONES_SELECTED 0         // If above is 0, value is index of array below.
+#endif                               // Etc/GMT0
+
 #define TIMEZONES_LENGTH 28
-#define TIMEZONES_SELECTED 0
 
 typedef struct TZ {
   const char* location;
@@ -22,44 +26,47 @@ typedef struct TZ {
 } TZ;
 
 
-#ifdef TIMEZONES_NON_GMT_OVERRIDE
 // https://raw.githubusercontent.com/nayarsystems/posix_tz_db/master/zones.csv
 static TZ tz_override = {
   "Europe/Madrid",
   "CET-1CEST,M3.5.0,M10.5.0/3"
 }; 
-#endif
 
 
 static TZ timeZones[] = {
-  {"Etc/GMT+0","GMT0"}, 		// 0
-  {"Etc/GMT+1","<-01>1"},		// 1
-  {"Etc/GMT+2","<-02>2"},		// 2
-  {"Etc/GMT+3","<-03>3"},		// 3
-  {"Etc/GMT+4","<-04>4"}, 		// 4
-  {"Etc/GMT+5","<-05>5"}, 		// 5
-  {"Etc/GMT+6","<-06>6"}, 		// 6
-  {"Etc/GMT+7","<-07>7"},		// 7
-  {"Etc/GMT+8","<-08>8"},		// 8
-  {"Etc/GMT+9","<-09>9"}, 		// 9
-  {"Etc/GMT+10","<-10>10"}, 		// 10
-  {"Etc/GMT+11","<-11>11"},		// 11
-  {"Etc/GMT+12","<-12>12"},		// 12
-  {"Etc/GMT-0","GMT0"}, 		// 13
-  {"Etc/GMT-1","<+01>-1"},		// 14
-  {"Etc/GMT-2","<+02>-2"},		// 15
-  {"Etc/GMT-3","<+03>-3"},		// 16
-  {"Etc/GMT-4","<+04>-4"},		// 17
-  {"Etc/GMT-5","<+05>-5"},		// 18
-  {"Etc/GMT-6","<+06>-6"}, 		// 19
-  {"Etc/GMT-7","<+07>-7"}, 		// 20
-  {"Etc/GMT-8","<+08>-8"}, 		// 21
-  {"Etc/GMT-9","<+09>-9"}, 		// 22
-  {"Etc/GMT-10","<+10>-10"}, 		// 23
-  {"Etc/GMT-11","<+11>-11"}, 		// 24
-  {"Etc/GMT-12","<+12>-12"},		// 25
-  {"Etc/GMT-13","<+13>-13"},		// 26
-  {"Etc/GMT-14","<+14>-14"},		// 27
+  {"Etc/GMT+0","GMT0"},         // 0
+  {"Etc/GMT+1","<-01>1"},       // 1
+  {"Etc/GMT+2","<-02>2"},       // 2
+  {"Etc/GMT+3","<-03>3"},       // 3
+  {"Etc/GMT+4","<-04>4"},       // 4
+  {"Etc/GMT+5","<-05>5"},       // 5
+  {"Etc/GMT+6","<-06>6"},       // 6
+  {"Etc/GMT+7","<-07>7"},       // 7
+  {"Etc/GMT+8","<-08>8"},       // 8
+  {"Etc/GMT+9","<-09>9"},       // 9
+  {"Etc/GMT+10","<-10>10"},     // 10
+  {"Etc/GMT+11","<-11>11"},     // 11
+  {"Etc/GMT+12","<-12>12"},     // 12
+  {"Etc/GMT-0","GMT0"},         // 13
+  {"Etc/GMT-1","<+01>-1"},      // 14
+  {"Etc/GMT-2","<+02>-2"},      // 15
+  {"Etc/GMT-3","<+03>-3"},      // 16
+  {"Etc/GMT-4","<+04>-4"},      // 17
+  {"Etc/GMT-5","<+05>-5"},      // 18
+  {"Etc/GMT-6","<+06>-6"},      // 19
+  {"Etc/GMT-7","<+07>-7"},      // 20
+  {"Etc/GMT-8","<+08>-8"},      // 21
+  {"Etc/GMT-9","<+09>-9"},      // 22
+  {"Etc/GMT-10","<+10>-10"},    // 23
+  {"Etc/GMT-11","<+11>-11"},    // 24
+  {"Etc/GMT-12","<+12>-12"},    // 25
+  {"Etc/GMT-13","<+13>-13"},    // 26
+  {"Etc/GMT-14","<+14>-14"},    // 27
 };
 
+static long OFFSETS_SEC[] = {
+  0, 3600, 7200, 10800, 14400, 18000, 21600, 25200, 28800, 32400, 36000, 39600, 43200, 0, -3600, -7200, -10800, -14400, -18000, -21600, -25200, -28800, -32400, -36000, -39600, -43200, -46800, -50400
+};
+
+static int8_t tzIndex = TIMEZONES_SELECTED;
 #endif //TIMEZONES_GMT_H
\ No newline at end of file