You want to work out sine calculations, in your head, whilst trying to fly and intercept to an ILS? Luvvaduk! Do what everybody else does- just get the aeroplane in the right configuration in near enough the right place and concentrate on flying it right! Leave the sliderule calculations to someone else! You just get a 'feel' when to do the right thing at (almost) the right time. Don't do sums in your head!