It is Tom's exactitude which allows him to reenter the window of his eleventh floor apartment after rashly stepping out on the building's ledge in order to retrieve the yellow sheet of paper on which he has made times-taking calculations. For, he knows that he has but one chance: He calculates against bringing his arm over his head, as a blow from such a position would not have enough force, and it would be so awkward that he would surely fall. Tom realizes that he must drive a blow from his shoulder, but he does not know if his fist will be able to break the glass. So, he pauses, contemplating his plan of action. Then, he knows that he must act; thinking of his beloved wife Clare, he draws back just a little with his fist so tight that his fingers ache. With all his power, he burst through the window thinking of Claire:
...with every last scrap of strength he could bring to bear, he shot his arm forward toward the glass, and he said, "Clare!"
He heard the sound, felt the blow, felt himself falling forward, and his hand closed on the living-room curtains, the shards and fragments of glass showering onto the floor.
As Tom breaks off the remaining wedges of glass from the window frame, he enters the room, "grinning in triumph."