Like most programs, there are several different ways to get to a desired end result. If you want to draw a tapered line, you can draw a line and apply a width profile to it or use a brush. I think what can be confusing is that some brushes don't use the width profile. There are multiple types of brushes (Calligraphic, Scatter, Art, Bristle, and Pattern). If you're selecting the Paintbrush with its defaults (Stroke: 1px, Width Profile: Uniform, and Brush Definition: 3 pt. Round), you'll draw a 1 pt. curve. If you select it and change the Width Profile, you won't see any difference either--even if you increase the stroke to 10 px. Now change the Brush Definition to Basic. Now, you should see the tapered ends applied to your curve. You can adjust the amount of width after a line is drawn. Select the line with the Selection tool (V), and change to the Width tool (Shift + W). Now click anywhere on the line and drag to adjust the line width. But you want to draw with this tapered effect, avoid the blue dots when drawing, and apply pressure with a Wacom tablet. You'll need to create a Calligraphic Brush. On the Brushes panel, click the New Brush button at the bottom, and create a Calligraphic Brush by clicking OK. In the Calligraphic Brush Options dialog that opens, look at the last attribute --Size. Make the brush whatever size you like, then change Fixed to Pressure. Adjust the variation to make the correlation between the pressure you apply and the change in the size. Look at the preview above the settings to see if it's how you'd like it set.
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