Residential window rough opening field measurement tutorial: what to check before installation

Before installing residential windows, even a slight discrepancy in the rough opening can affect waterproofing, shimming, and the plumbness of the window frame. I've seen crews order based solely on blueprint dimensions, only to find the opening 1/2 inch too wide on-site, which made the subsequent flashing and trim look terrible. My field measurement process involves measuring the width at the…