In reply to Abhyudha:
The `timescale compiler directive specifies the default time unit and precision for all design elements that follow this directive and that do not have timeunit and timeprecision constructs specified within the design element.
Defining the timeunit and timeprecision constructs within the design element removes the file order dependency problems with compiler directives. There shall be at most one time unit and one time precision for any module, program, package, or interface definition or in any compilation-unit scope. This shall define a time scope.
You can also checkout the precedence of timeunit, timeprecision, and `timescale in LRM.