Size & Orientation
In addition to contextual behaviours (Reading Distances), a landscape or portrait orientation change of a device can also affect the layout of an application.
Content column widths that vary in each case, will also change line length and the number of characters available for each line. Ideally, if a limit of 12-15 words is set per line as a standard, the font size will need to increase or decrease, in proportion to the column width to achieve optimum readability. See examples below:
Standard Body Copy Size (Extra Small Measure)
with Optimum Column Width 450pt (approx)
Enlarged Body Copy size (Medium Measure) as a result of new orientation
with new Optimum Column Width 600pt (approx)