# Determine Rise In this section, we will determine the RISE using 2 different methods.

Here, we will determine the RISE (line “AD”) of an arc if we know the RADIUS and the ARC LENGTH.

This exercise is useful for measuring your target curvature when rolling large radii with relatively short arc length.

Our Radius will be 300″ and the Arc Length will be 240″
300″ x ∏ = 942.4778″
Now 942.4778″ ÷ 240″ = 3.927  Now 1/x  you get .25465
Now x 180º = 45.8366º  Now 45.8366º ÷ 2 = 22.9183º
Now COS – 1 = -.07894  Now x 300″ = 23.6817″

In short:

Radius x ∏ = ___  ÷ Arc Length = ___  1/x ___ x 180 = ___ ÷ 2 = ___ COS – 1 = Rise

NOTE: The negative number here does not matter.

This exercise is good for all angles of less than 180 degrees of arc.

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Here, we will determine the RISE (line “AD”) of an arc if we know the RADIUS and the CHORD.

Our Radius  will be 60 inches and the Chord “BC” will be 96 inches.
60 ² – 48 ² = 1296 now (square-root). You get 36.
Now 36″ – 60″ = 24″.
The RISE (line “AD”) of this arc is 24 inches.

In short: