hitch has been used to tie off tennis string, along with a starting knot. Recently, new kinds of knots have been used called the "pro-knot" and "Parnell knot". Along with the use of a starting clamp, this can make all the knots identical, and improve the aesthetics of a string job. Stringing The process of installing strings in the racquet is called "stringing," and is done with a racquet string machine. These machines vary in complexity, accuracy and price. String tension The "string tension" of a racquet, usually expressed in pounds, indicates the pressure under which the strings are secured to the frame. The string tension affects a racquet's playing characteristics, such as the "feel" of the ball, control over the ball, as well as maximizing power. All racquets come with recommended string tensions, most of which lie between 50 and 70 pounds (220 to 310 N). A loosely strung racquet will usually have a larger sweet spot and will hit farther but, when swung hard enough, it will shoot balls unpredictably; a tighter string job will help make delicate shots with more finesse and control. An extremely tightly strung racquet cuts down on a tennis player's feel on the ball, but can give the player excellent control if swung hard enough, with a smooth stroke. Such tension may make delicate shots more difficult, but makes play from the baseline more constant. However, if a player often hits powerful shots, a tightly strung racquet may quickly tire the arm, possibly resulting in tennis elbow. Many professional stringers advise players to string racquets with the lowest tension possible while still being able to maintain control of the ball. Beginning players trying to find their tension should start in the middle of the recommended tension range and adjust the tension from there to meet their needs. The recommended tension is usually printed on the racquet. With a lower tension the racquet will have more power and less control; with a higher tension, it will have less power and more control. Restringing Due to the tension present on the strings, elasticity and tension begins to decrease the moment they are installed in a racquet. "Dead strings", or strings which have lost their tension, cut down on the performance of a racquet. Dead strings may also hamper a tennis player's ability to generate power and pace, and may even make their arm sore. The