Subtract the angle given in the sun angle table from 90° (since most protractors have 90° as the vertical point). For example, the given angle at latitude 36° North at 10 a.m. is 24°, so you would calculate 90°-24°=66°.
• Hold the protractor so the flat side is at the top and tilt it until the wire hangs down at the calculated angle. In our example, that's 66°.
• Point the protractor where the sun will be at the time of day for which you're calculating things (10 a.m. in our example) and sight along the flat edge.
• If you see anything but sky, it's very likely an obstruction to your solar window.
• Repeat this process for every hourly sun position from 9:00 a.m. to 3:00 p.m.

Although this method is clunky and inaccurate, it's easy to do with some very low-cost equipment and can serve as an initial survey to eliminate bad sites.