[Zeke]

Andersen was always weird. The RO for old fashioned wood sash windows followed a couple of formulas depending on whether it was a double hung or casement. In the case of the DH it was the overall sash size that was the call out. So you would add 2" to the width and 4 to 4 1/2" to the height.

That was a new construction window which is not the subject at hand.

Old wood casement windows could be either swing in or swing out. You don't see wood SI casements these days because they leak. But the RO was different for each. My biggest problem replacing original wood sash casements was retro fitting with a historically correct window when the old casement had already been taken out in favor of a 60's and 70's AL insert window.

Architectural standards today call for RO's to be nominal, e.g., even numbers in 6 inch increments starting at 12". Some of the old line companies are not in step.