It's a moonlit December night in 1971. An English Electric Canberra BI8 (along with four others) takes off from an inland Air Force base. The 5 cockpit clocks and the 10 pilots' and navigators' hacking HMT wristwatches have already been synchronised. You land at a forward base, just miles from the border. A quick refuel, latest updates, last briefing from the leader and you are off. You climb to 1000 ft. Soon, you are over enemy territory. Navigation is visual (a bend in the river, a bridge, anything distinctive). You consult your trusty HMT (or the cockpit clock) and make the necessary corrections (power up or down if you are too late or too early at a waypoint, bank left or right if you are off course).
You can see the initial point in the distance and you pull out the crown on your HMT when the second hand crosses 12. At the initial point (visual) you push in the crown. Now you fly level at a precise speed. At 2 minute 45 seconds (as per your trusty HMT) you pull up to bombing height, which is 6000 ft. At 3 minutes 45 seconds you level out. Your navigator can see the target and he takes over, the HMT has served it's purpose. He guides you till he has the target in his sights. He releases the bombs.
You fly full speed out of the umbrella of flak. Once out of it you quickly descend to 1000 ft. You fly full speed till you are out of enemy territory. The HMT can still be used to time intervals but not to know the exact time. The cockpit clock will tell you that. Once you are back over friendly territory, the ground radar unit checks your tail and, if clear, you ascend to 20,000 ft., reduce speed to conserve fuel and head back home. Every last thing, including your watch, worked in your favour today