Calculating daylight remaining

Like a small number of people I do struggle with "Telling the time" which was a bit of an issue in very timetable settings such as school but there are otherways of working out roughly how much daylight you have and from that having some idea of time of day.

While the source of this illistration isn't one I endorse, it is actually really useful if you are out and let's say your watch fails or worse still gets lost.