00:00 -- Total differential: re-writing to introduce "nabla" (aka "del") operator
06:45 -- Directional derivatives and the fact that the gradient of a function gives the direction of fastest change in the function
15:50 -- Examples of calculating directional derivatives
19:09 -- Steepest way up Slemish
24:42 -- A comment that a simpler example would be finding the direction of the fastest increase in the temperature in a room (likely to be in the direction towards the radiator)
26:05 -- Napoleon's nose in north Belfast (Cavehill)
