How do I determine the processor speed?

function GetCPUSpeed: String;
const
  DelayTime = 500;
var
  TimerHi, TimerLo: DWORD;
  PriorityClass, Priority: Integer;
  Speed: Double;
begin
  PriorityClass := GetPriorityClass(GetCurrentProcess);
  Priority      := GetThreadPriority(GetCurrentThread);

  SetPriorityClass(GetCurrentProcess, REALTIME_PRIORITY_CLASS);
  SetThreadPriority(GetCurrentThread, THREAD_PRIORITY_TIME_CRITICAL);

  Sleep(10);
  asm
    dw 310Fh
    mov TimerLo, eax
    mov TimerHi, edx
  end;
  Sleep(DelayTime);
  asm
    dw 310Fh
    sub eax, TimerLo
    sbb edx, TimerHi
    mov TimerLo, eax
    mov TimerHi, edx
  end;

  SetThreadPriority(GetCurrentThread, Priority);
  SetPriorityClass(GetCurrentProcess, PriorityClass);

  Speed := TimerLo / (1000 * DelayTime);
  if Speed >= 1000 then
    Result := FloatToStr(RoundTo(Speed/1000, -2)) + ' GHz'
  else
    Result := FloatToStr(RoundTo(Speed, -2)) + ' MHz';
end;