The area on your racquet's string bed in which hitting the ball does not produce uncomfortable vibrations is called the node of the first harmonic. That sweet spot is where hitting the ball feels good.

Difficulty Level: easy      Time Required: 5 minutes

1. Place an ordinary index card against either of the faces of your racquet handle that are parallel to the plane of your strings.
2. Position the index card so that 2/3 of its length extends beyond the end of the racquet butt.
3. Apply a piece of tape perpendicular to the boundary between the edge of the index card and the racquet handle, extending one inch onto each surface.
4. Hold the racquet with the butt pointing straight up.
5. Apply another piece of tape that starts on the (horizontal) butt cap, then makes a 90-degree turn upward and attaches to the lower middle of the index card. Leave a little slack.
6. Hold the racquet loosely, butt end up, between your thumb and forefinger, 6 inches below the butt end.
7. Bump the butt end of a second racquet against your string bed, causing the first racquet to swing back and forth like a pendulum.
8. Bump near the tip of your racquet and note that the index card buzzes loudly.
9. Bump near the throat of your racquet and note that the index card buzzes, but less loudly than at the tip.
10. Keep bumping the string bed in different locations. Your harmonic sweet spot is the area of you string bed in which bumping does not make the index card buzz.
    

1. If you can't produce a buzz anywhere, this does not, unfortunately, mean you have the world's biggest sweet spot. You probably taped the index card too tight.
2. Hitting the harmonic sweet spot can greatly reduce arm fatigue and irritation.
3. See the links below for how to find your other two sweet spots.
   

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