Function GASDEV:real;
var
   V1,V2,FAC,R:real;
begin
    If ISET^= 0 Then
    begin
      repeat
        V1:=2 * Random - 1;
        V2:=2 * Random - 1;
        R:=Sqr(V1) + Sqr(V2);
      until (R < 1);
      FAC:=Sqrt(-2 * Ln(R) / R);
      GSET^:=V1 * FAC;
      GASDEV:=V2 * FAC;
      ISET^:=1;
    end
    Else
    begin
      GASDEV:=GSET^;
      ISET^:=0;
    end;
end;