Visible Transmittance (VT) and Condensation Resistance (CR):

Visible Transmittance (VT):

Visible Transmittance is simply the amount of visible light that a window allows into the room. The higher the VT, the more light passes through the window. It is often difficult to tell the difference in windows with similar VT ratings. Before making VT a major deciding factor, it is best to look at a sample window as differences are usually barely noticeable. 



Condensation Resistance (CR):

CR measures how well a window resists the formation of condensation on the inside surface. CR is expressed as a number between 1 and 100. The rating value is based on interior surface temperatures at 30%, 50%, and 70% indoor relative humidity for a given outside air temperature of 0 degrees Fahrenheit under 15 mph wind conditions. The higher the number, the better a product is able to resist condensation. CR is meant to compare products and their potential for condensation formation.
http://www.efficientwindows.org/cr.php