Distance Time 4 4 4 4 4 6 6 6 6 6 8 8 8 8 8 10 10 10 10 10 6 6 6 6 4 7 6 6 3 6 5 3 3 2 5 6 4 4 2 3 Source: Douglas C. Montgomery, "Design and analysis of experiments", 5th ed., John Wiley and Sons, 2001 Data are lengths of time required (in milliseconds) for the human eye to focus on a suddenly revealed object, at distances of four, six, eight, and ten meters. xperiments"