sentences:  These methods involved either training a continuous beam of visible light onto the eye to produce an unbroken line on photographic paper, or a flashing light to produce a series of white spots on photographic paper at sampling intervals around 25 ms (i.e., 40 samples a second).Because the film rolled through the device vertically, the vertical movement of the eyes in their journey across the page was either unrecorded or was recorded using a second camera and subsequently combined to provide data on both dimensions, a cumbersome and inaccurate solution.These systems were sensitive to even small movement of the head or body, which appear to have significantly contaminated the data.