why is the standard meridian selected by a country a multiple of 7.5 degree ?

IN ANCIENT TIMES, SUN WAS THE ONLY MEANS TO TELL THE TIME. PEOPLE USED TO SEE THE PATH OF THE SUN IN THE SKY TO ESTIMATE THE TIME. THE EARTH ROTATES FROM WEST TO EAST AND COMPLETES ONE ROTATION IN 24 HOURS. THIS ALSO MEANS THAT 360 DEGREES LONGITUDES FACE THE MID DAY SUN ONE AFTER THE OTHER IN 24 HOURS. THUS, 15 DEGREE LONGITUDE PASSES BEFORE THE SUN IN A PERIOD OF 60 MINUTES OR 1 HOUR. FURTHER, IT TAKES 4 MINUTES TO CROSS ONE LONGITUDE BEFORE THE SUN. THIS IS THE LOCAL TIME. LOCAL TIME MEANS THAT TIME WHICH IS SELECTED FOR EVERY VERTICAL LINE OF LONGITUDE.

ALL PLACES LOCATED ON DIFFERENT MERIDIANS HAVE DIFFERENT LOCAL TIME. IT WOULD CREATE A LOT OF DIFFICULTIES, IF ALL COUNTRIES WOULD HAVE ADOPTED DIFFERENT LOCAL TIME. THE RAILWAY TIME TABLE AND THE SHEDULES OF THE AIR FLIGHTS WOULD BE DIFFICULT TO PREPRARE. PEOPLE CROSSING THE LONGITUDES WOULD HAVE TO ADJUST THIER WATCHES. INDIA LIES BETWEEN 68 DEGREES EAST AND 97 DEGREE 25 MINUTES EAST LONGITUDES. THE PEOPLE OF INDIA WOULD FACE A LOT OF PROBLEMS IF THEY FOLLOWED DIFFERENT LOCAL TIMES.

IN ORDER TO AVOID THIS PROBLEM AND MAINTAIN ITS UNIFORMITY ALL OVER A COUNTRY, IT WAS DECIDED TO ADOPT THE LOCAL TIME OF A CENTERAL MERIDIAN OF A COUNTRY AS THE STANDARD MERIDIAN TIME. THE MERIDIAN SELECTED, SHOULD BE DIVISIBLE BY 7.5 DEGREE SO THAT THE DIFFERENCE BETWEEN ITS STANDARD MERIDIAN TIME AND THE GREENWICH MEAN TIME {GMT} IS EXPRESSED AS A MULTIPLE OF ' HALF AN HOUR' . THE MERIDIAN, SELECTED FOR A COUNTRY, IS CALLED THE STANDARD MERIDIAN.