FlightDetent... and others. I think there must still be some misunderstanding amongst pilots of how air traffic controllers actually function. Long, long ago I showed round a BA Command Course at Heathrow. During the Q&A sessions at the end one guy asked "where is the computer which tells you what headings to give us". I merely pointed at my head and he was duly amazed. Most of my UK expereince has been in busy LTMA airspace and up until the time I retired there was absolutely no computer assistance available which determined the timing and nature of instructions passed to pilots. There are tools for conflict alert and tools to provide information regarding flight plans to contollers but the actual decisions regarding instructions given to pilots are determined by the controller without any outside prompting (except when they are under training and a training officer maybe nudging them).
ATCOs are fully aware of the alt divided by range rule - they practice it every time they do their emergency training, but the question posed by this thread concerned the Heathrow Final Director. His method is to look at the radar display, count the aeroplanes and apply his skill and experience to determine the ranges from touchdown to be passed to the pilots.
At ALL times the controller decides this in his head - there is no external magic box which does it for him. Twice during my time at Heathrow we trialled computer assisted approach sequencing tools and rejected them either because they were unsafe or because they could not better a properly trained and experienced controller.