In the last paragraph "both" refers to: 

PART 1: READING COMPREHENSION

Based on the text below, answer the question.

Exercising Body and Mind at the Same Time?

New Device Lets You Read While You Run

Engineers from Purdue University have devised a new System that will facilitate a very specific type of physical and mental multitasking - helping treadmill runners to read text on a display screen.

The System, called ReadingMate, compensates for constantly bobbing eyes so runners can train for a marathon while reading their favorite novel. 

"Not many people can run and read at the same time," said Ji Soo Yi, an assistant professor of industrial engineering at Purdue University. "This is because the relative location of the eyes to the text is vigorously changing, and our eyes try to constantly adjust to such changes, which is burdensome."

Instead of increasing the size of the displayed font, Yi and his colleagues decided to compensate for a runner's head motion. 

"You could increase the font size and have a large-screen monitor on the wall, but that's impractical because you cannot have numerous big screen displays in an exercise room," Yi said. 

According to a report on the system published recently in Human Factors: The Journal of the Human Factors and Ergonomics Society, the engineers recruited 15 multitasking volunteers to perform a "letter-counting" test while jogging on a treadmill and using ReadingMate. The participants were asked to tally how many times the letter 'F' appeared in two lines of text nested in 10 lines of text that were displayed on a computer monitor.

While performing the test, the participants wore goggles equipped with infrared LEDs. An infrared camera tracked the motion of the LEDs, essentially recording the movement of the runner's head. To compensate for the head motion, the displayed text was moved as the volunteers ran along the treadmill with their heads bobbing. 

The researchers found those who used the ReadingMate system performed better at multi-tasking their physical and mental assignments, particularly when it carne to reading smaller font sizes and smaller line-spaced text. 

Besides aiding people with the novel task of reading while running, the researchers said their system could be used to assist airline pilots or those working in heavy industry.

"Both may experience heavy shaking and turbulence while reading information from a display," Kwon said. "ReadingMate could stabilize the content in such cases." 

(Adapted from http://www.redorbit.com/news)