Arched, angled, and half-round windows are where custom window treatments prove their worth, and where bad measurements show the most. A rectangle window can hide small errors behind a frame. A curve can't.
Very few arches are perfect segments of a circle. Builders frame them by hand, drywall adds its own variation, and the two sides are rarely identical. That's why we template arches on site, tracing the actual curve instead of calculating it from width and height alone.
Angled tops and trapezoids need every angle measured, not just the long sides. Bay windows need each plane measured separately, plus the angles where they meet, so frames join cleanly in the corners and panels can open without hitting each other.
If you have specialty windows, avoid ordering online from your own measurements. Book an in-home measuring visit instead. It's free with us, and it's the difference between a shutter that looks built-in and one that looks like it almost fits.