{/************************************************************************/}
{/* Wait for start of next vertical retrace				*/}
{/************************************************************************/}

procedure wait_4_vert;
var
i,count : word;
begin
	writeln('...counting');
	count := ticks;				{/* Get current tick	*/}
	for i := 0 to 299 do vertical_retrace;	{/* Wait for start of	*/}
						{/* next vertical retrace*/}
	count := ticks - count;
	writeln('300 vertical retraces took ',count,' ticks');
	writeln('That is a ',(300*longint(91)) div (5*count),' Hertz refresh rate');
end;