FOUR variables – x, y, z (three space variables) and t (one time VARIABLE). Each satellite corresponds to one variable. Therefore, to uniquely determine the position of the user using GPS minimum 4 satellites are required. However, if we use less than 4 satellite say 2 nos., then out of variable TWO variables say x and y are known and other two variables z and times are unknown and they can take many values i.e. we have MULTIPLE positions and hence, we are not able to determine the position of any object uniquely.