  The viewing size of a signer correlates with legibility, i.e., the ease with
which a viewer can recognize individual signs. The WCAG 2.0 guidelines (G54)
mention in the notes that there should be a mechanism to adjust the size to
ensure the signer is discernible but does not state minimum discernibility
guidelines. The fluent range (the range over which sign viewers can follow the
signers at maximum speed) extends from about 7{\deg} to 20{\deg}, which is far
greater than 2{\deg} for print. Assuming a standard viewing distance of 16
inches from a 5-inch smartphone display, the corresponding sizes are from 2 to
5 inches, i.e., from 1/3rd to full-screen. This is consistent with vision
science findings about human visual processing properties, and how they play a
dominant role in constraining the distribution of signer sizes.
