EBAY has a Ross Round System on the auction site.The frame dimensions are 13 3/4L X 20W X 4 1/2H. The 10 Frame Langstroth is 19 7/8 L X 16 1/4 W X 5 11/16 H. Does the Ross rounds come in differnet sizes? Do you think he measured wrong?
the ross system is smaller than a standard frame but uses spacers to reduce a shallow to hold the system. don't know if it was designed this way to accomodate many different hive dimensions used over the world or it is a part of allowing bee space and transit ways on the sides of the supers. the seller should provide the spacers
you can ask Lloyd (the owner of the Ross system):
Lloyd Spear <Lloyd@ROSSROUNDS.COM>