clock_t clock( void )

	- prototype in time.h

	- returns elapsed processor time used by the calling process,
	  or -1L on error
	- C startup code retrieves the clock count as preparation for a 
	  later call to clock()  (Turbo C++ and some versions of MS C)
	- resolution is limited to 54ms for both MS C and Turbo C due
	  to the dependency on INT 8 clock tics
	- CLK_TCK is shouldn't be used unless CLOCKS_PER_SEC isn't available
	  since the latter is defined by ANSI.
	- MS C uses INT 21,2C to get the processor time with 1000 as the
	  value of CLK_TCK
	- Turbo C uses INT 1A,2 to get the processor time with 18 as the
	  value of CLK_TCK

	- Example usage:

	  clock_t start, finish, duration;
	  start = clock();
	  finish = clock();
	  duration = finish - start;
	  printf("%ld - %ld = %ld tics\n", start, finish, duration);