http://gbnsr.org.uk/cft/VFR%20Naviga...Technique.ppsx
Above is a link to the Standard Closing Angle technique. Very very simple to use in practice. Just need to know actual True Airspeed and cross track error as a distance and a watch ⌚️. Amount of mental arithmetic needed is very little. However it does assume compass and DI aligned and you set course accurately over your turning point. Cheers Phil