Super Easy Method to layout trim angles using 90° weld elbows. 

Yes - instead of 1 inch = 1 degree at a 57.3 inch radius, you can use a radius of 28.65 inches and have 1/2 inch = 1 degree or a radius of 14.325 inches for 1/4 inch = 1 degree. A folding ruler works very well for this.; Simply drill a small hole at the 1 inch mark which, another at (14.325 + 1inch), another at (28.65 + 1 inch) and the last at (57.3 + 1 inch) this gives you three options - just be sure you use the correct measurements along the arch when converting to degrees. You could use a permanent marker to write the inch/degree value on the folding ruler near the hole...... Hold a nail in the hole placed at 1 inch ( the center of the circle) and a pencil in one of the other holes to draw the arc. Then measure along the arc as shown in the video - the folding rule will bend along the 57.3 inch radius but not the smaller radius values.

If you have a question or if something is unclear, let me know how I can help.

The steps on how u started that

Since your request wasn't more specific and constructing the lines and arc are easy enough, I'll assume you are wondering how the 57.3 radius was determined. A circle has a circumference = 2*PI*Radius and 1/4 of a circle equals 90 degree so > 90 degrees = (2*PI*Radius)/4 and solving for the Radius we get R=(90*4)/(2*PI) which equals 57.3 inches. Does That clear things up for you?

To be correct, I wanted the arc to be 1" for each degree such that 90 degrees would equal 90 inches along the circumference.