Readability is the ease with which text can be read and understood. Various factors to measure readability have been used, such as "speed of perception," "perceptibility at a distance," "perceptibility in peripheral vision," "visibility," "the reflex blink technique," "rate of work" (e.g., speed of reading), "eye movements," and "fatigue in reading."Readability is distinguished from legibility which is a measure of how easily individual letters or characters can be distinguished from each other. Readability can determine the ease in which computer program code can be read by humans, such as through embedded documentation.