1.  Field of the Invention. 
The field of the invention is means for fixing the fingering of a guitar string or other fretted stringed musical instrument string. 
2.  Description of Related Art. 
In guitars and other fretted musical instruments, one or more strings are stretched under tension across a sounding board or other main body of the instrument which, upon the string vibrating, amplifies the sound of the vibrating string.  One end of the string is anchored at one side of the main body or sounding board, the string then strung across the sounding board, and along an elongated neck portion attached to the main body.  The other end of the string is then anchored at the end of the neck away from the main body to tuning pegs or other devices which permit adjustment of the string tension.  At variously determined intervals along the neck portion are situated a plurality of frets, i.e., transverse ridges which underlie the plurality of strings, which frets are in turn resting upon a fretboard. 
The strings do not touch the frets, even during vibration. 
The sound emitted from a plucked string is termed its pitch and is determined by the relationship of the tension of the string, its mass per unit length (which is a function of the string's diameter), and the length of the string available for vibration (effective length).  The effective length of the string is the distance between a first anchor, called the bridge, attached at the head of the main body of the fretted stringed instrument, and a second anchor, called the string nut, attached at the far end of the neck.  Many times, all the strings ride over a saddle which is immediately adjacent to the bridge.  The effective length in which case then starts at the saddle.  At the neck far end is the second anchor, the string nut, over which all of the strings pass and contact immediately before they are attached to the tuning pegs. 
On guitars or other fretted stringed musical instruments it is common for the musician to use his hand not plucking or striking the strings to press upon one or more strings of the instrument with one or more fingers to cause the string to engage the frets along the neck of the guitar or other musical instrument. 
To easily change the pitch of the string, one merely shortens the string.  To accomplish this, the player need only to press down on the string to cause it to engage one of the frets on the fretboard portion of the neck of the instrument.  This procedure reduces the effective string length to the distance between the saddle and the fret.  As a general rule, the 12th.  fret on a guitar is located one-half of the distance between the saddle and the string nut.  Then, if the string is held at the 12th.  fret, the pitch doubles.  A violinist or guitar player is constantly fingering the instrument as he plays it, using the fingers of the hand not plucking the strings (or drawing a bow across the strings) to change the pitch as called for by the musical score. 
A prior invention by the instant inventor for a positioner acting as a fixed fingering device was granted by the United States Patent Office on Jan. 17, 1989 and accorded U.S. Pat.  No.  4,789,119 concerned threaded inserts strategically placed in the fretboard, the inserts receiving machine screws which cupped the string under its head.  By screwing down the machine screw securely into the insert, the screw would secure the string over the fret.  However, such device, while very adequately performing the job, took some period of time for the player to unscrew the screws to a position above the height of the string, and then screw the screws down over the string.  Such adjustment might easily be made between musical numbers, however, perhaps it did require too much time to secure a string during a musical number or, during the musical number, to unsecure a string. 
It has been determined that it would be useful to have a device which mechanically fingers one or more strings of a stringed instrument for a changed, but constant pitch, during a whole musical number or a portion of one while at the same time making the remainder of the instrument strings, including the mechanically fingered string, still available for further non-mechanical fingering by the musical player.  It is to this invention that the subject patent is directed. 
It would also be useful if such a device could be placed or removed in a very short period of time, perhaps in less than a second or two.