res 1 or RES : Symbol for "resolution," a unit defined to be the number of dots or pixels per millimeter in an image. The unit is often stated before the measurement. RES 1 is equal to 25.4 dots per inch (dpi)
Russ Rowlett (Director), How Many? A Dictionary of Units of Measurement, Center for Mathematics and Science Education University of North Carolina, USA 2005. http://www.unc.edu/~rowlett/units/dictA.html, (Unit of Meas and Covr Factors - Amer) {608}