Think about the person that uses prescription eyeglasses…
As they put them on, their speed of accurate reading immediately increases.
Some people question whether or not text format changes (such as size, shape, and spacing) can significantly impact readability. A reader with the perfect pair of glasses offers an analogy. For readers who need them, the glasses provide instantaneous change to text readability. Likewise, making subtle changes in text format for the individual can deliver immediate, meaningful improvement in reading speed and accuracy.
Using readability features to change text format can make both adults and children faster, more accurate readers. These changes can increase an adult’s speed of accurate reading by 20% or more, and that of children up to 50% or more. The bottom line is that there is no single best font or text format for reading; instead, there is an optimal reading format for each individual.
Tune Your Text: Adjust it; read with your own best format.
Expecting one text format to be best for all readers is like expecting there is a single eyeglasses prescription that is best for all people.
– Marjorie Jordan, Readability Matters