Boston ? The pencil scribbles on a yellow legal pad suggest an impending crisis.

Over and over, John F. Kennedy wrote the words “decisions” and “leaders” on his pad as his advisers debated the next step in the Cuban Missile Crisis. In the middle of the sheet of paper is a set of concentric circles — perhaps representing a blockade of Cuba.

That sheet of paper is among the artifacts displayed at the John F. Kennedy Library and Museum in an exhibit marking the 40th anniversary of the Cuban Missile Crisis.

The exhibit features a 20-minute film of newsreels, television news footage and a December 1962 TV interview with Kennedy, as well as correspondence between Kennedy and Soviet Premier Nikita Khrushchev, showing how relations between the two men evolved during the 13-day crisis.

But Kennedy’s doodles on yellow paper a habit of his, museum curator Frank Rigg says seem to have the most resonance with visitors.

“Looking at his own scribbled notes he was just like an average person sitting in a serious meeting,” says Peggy Beltramo, 54, of Los Gatos, Calif., who was visiting the library with her husband. “It’s very personal.”

Rigg says he hopes visitors come away with “a sense of how Kennedy remained open to discussion and different viewpoints how he did not jump in and take the most obvious course (of air strikes or invasion) right away.”

“I hope visitors get a sense of how Kennedy and Khrushchev responded to this crisis. Those two men held the fate of the world in their hands.”

The exhibit traces the timeline of the crisis with photos, meeting minutes and letters to and from Kennedy. They include an outline of plans to carry out air strikes against Cuba, meeting minutes in which advisers weigh the possible consequences and Kennedy’s televised address to the nation on Oct. 22.

In a letter to Khrushchev, Kennedy explains his Oct. 22 speech to the nation and makes his position clear: The U.S. will not back down.

“The one thing that has concerned me has been the possibility that your government would not correctly understand the will and the determination of the United States,” he writes. “I have not assumed that you or that any other sane man would, in this nuclear age, deliberately plunge the world into war.”

Four days letter, Khrushchev, toning down the volume and the rhetoric, offers to withdraw the missiles from Cuba if the U.S. pledges not to invade Cuba.

The letter is known as the “knot letter” because Khrushchev said if two sides kept pulling on the “knot of war,” it would be pulled so tight only war could break it. “War ends when it has rolled through cities and villages, everywhere sowing death and destruction,” he wrote.