Exercise 2: sample answer

Sundial. Strength: needs no fuel or maintenance and is accurate to a few minutes when well made. Weakness: useless at night and under cloud.

Outflow water clock. Strength: works day and night, indoors. Weakness: the flow slows as the level falls and changes with temperature, so it drifts and must be checked.

Candle clock. Strength: simple, portable and works at night. Weakness: draughts and uneven wax change the burn rate, and it is used up.

For a night watch I would choose the candle clock, because it is cheap, needs no skill and shows how much time has passed since it was lit; a water clock would be a good second choice if kept somewhere still. A sundial cannot be used at all.