INTERACTIONS.ACM.ORG 56 INTERACTIONS JULY–AUGUST2014 FORUM LET'S GET PHYSICAL

must give an interception heading clearance to another aircraft to let it rejoin the landing pattern. As a physical reminder, she holds the EZY4262 strip in her left hand so she won’t forget to send it to the tower controller.

Augmented strips as a mix of virtual and physical media. The system provides a hybrid artifact, in which paper and digital media are identical and have equal importance.

When one controller holds a paper strip, the other controllers can use the digital pen to interact with its virtual twin: They can write on it or move it by dragging on its border.

When repositioning the paper strip on the board, the virtual strip is aligned under it. The then obscured handwritten notes of the virtual strip are projected onto the paper strip. The system lets the controller extend the physical strip virtually.

Thirty minutes later, the traffic gets quite intense, so Tessa’s sector needs to be split up. Two colleagues are on standby in the control room. Tessa initiates the degrouping mode in the system. She decides to hand off the area around the MOLEK beacon, picks up the strips of the flights that are in this area, and gives them to Patrick, the planner of this new sector.

During this phase, the virtual twins of the removed strips remain displayed on her board. Until Patrick tells her that he is ready to control the corresponding aircraft, she continues to control them with their virtual strips, rearranging them on the stripboard and writing clearances as necessary. The entered information is simultaneously projected onto the corresponding physical strips on Patrick’s stripboard. Later, the crew of a recently departed aircraft calls to signal a sick passenger and report they must return to the airport. Tessa wants to note the problem on the corresponding strip, but it is already quite full. She chooses to enlarge the physical strip with a virtual

spatial arrangements of strips help manage their workload [ 2, 5]. Some tacit guidance on the given clearance level may also have been provided through physical manipulations of the strip.

Tessa is right-handed and must hold the strip with her left hand to write on it.

Therefore she knows instinctively that she has circled a high level, as its value is located at the bottom right of the strip.

By contrast, since virtual strips do not need to be held, they do not trigger this type of embodied memory.

Now the lowest aircraft in her sector, easyJet EZY4262, is five nautical miles from the runway. She needs to transfer control to the tower controllers, but more urgently, she

(Top) A controller collaboratively optimizes an arrival sequence, using a paper strip, numeric pen, and projected information. (Bottom) Free-hand writing and drawings convey key information.

The system provides a
hybrid artifact, in which
paper and digital media
are identical and have
equal importance.

strip. The system acknowledges this order and signals it as consistent by highlighting the drawn circle in green (the feedback would have been red in case of an inconsistent clearance, for instance a new level above 90).

Enabling input from paper through OCR. Tessa also asks TH Y1825 to turn to heading 340. She writes 340 on the strip.

The system recognizes the entered
values and can use it to check that there
is no risk of collision with other aircraft.

Fostering embodied cognition.

With Strip’ TIC, controllers can keep interacting in the physical space and rely on externalization to decrease their cognitive load [ 4]. For instance,