Had a very well known FOI, (later ATO), for checks many years ago, and his forte was in asking for rule-of-thumb or guesstimates for such questions as:
1. what does each 5 kts of tailwind do to your landing or takeoff distance ?
2. what does flying at 45% power instead of 65% do for your endurance ?
3. what does each 1000 ft elevation add to your take-off distance ?
4. if your tyres are leaving obvious tracks in the surface - what % extra distance will be required for take-off ?
I reckon it's a sign of experience and common sense for a testing officer to ask this sort of stuff because the student is going to learn from it.
happy days,