How to Make a Sigmoidal Curve in Illustrator CS5
A sigmoidal, or sigmoid, curve is an S-shaped curve that shows a slow rate of increase, then a high rate of increase, followed by a decrease. It is often used to show a learning curve or show retail sales trends. You can use the Pen Tool in Adobe Illustrator CS5 to create a sigmoid curve.
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Instructions
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1
Open a new document in Adobe Illustrator CS5. Select the “Pen Tool” from the Toolbox.
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2
Move the Pen Tool to the left side of the document, about halfway down. Click and hold the mouse button to create the first anchor point.
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3
Drag the mouse up toward the center of the document at about a 30-degree angle. This creates the slope angle of the first curve. Release the mouse button. Note that the slope line is visible. The slope line dictates the degree of slope in each curve between two anchors. The end of each slope line is called a handle.
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4
Position the Pen Tool near the top of the document, above the handle of the slope line you created in Step 3. Click and hold the mouse button. The first part of the curve is now visible, showing a slow increase, then a steep increase in the curve.
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5
Drag the mouse slowly toward the right edge of the document. This creates a leveling-off effect at the top of the curve. Release the mouse button when this part of the curve looks right for your purposes.
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6
Position the Pen Tool on the right side of the document where you want the curve to end. Click and hold the mouse button. This creates a downward curve. Drag the mouse to the right to create a tapering-off effect.
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7
Edit the shape of the curve as needed by using the Direct Selection Tool located in the Toolbox. Click any anchor point to change its position. Click on any slope line handle to change the degree of curve. You can also click the sigmoidal curve to change its shape.
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