The patent file contains at least one drawing executed in color. Copies of this patent with a color drawing will be provided by the Office upon request and payment of the necessary fee.
  
    FIG. 1 is a perspective view of an instrument showing a first embodiment of our new and ornamental design;
  
    FIG. 2 is an alternate perspective view thereof;
  
    FIG. 3 is an alternate perspective view thereof;
  
    FIG. 4 is an alternate perspective view thereof;
  
    FIG. 5 is a rear elevation view thereof;
  
    FIG. 6 is a front elevation view thereof;
  
    FIG. 7 is a side elevation view thereof;
  
    FIG. 8 is a side elevation view thereof;
  
    FIG. 9 is a top plan view thereof;
  
    FIG. 10 is a perspective view of an instrument showing a second embodiment of our new and ornamental design;
  
    FIG. 11 is an alternate perspective view thereof;
  
    FIG. 12 is an alternate perspective view thereof;
  
    FIG. 13 is an alternate perspective view thereof;
  
    FIG. 14 is a rear elevation view thereof;
  
    FIG. 15 is a front elevation view thereof;
  
    FIG. 16 is a side elevation view thereof;
  
    FIG. 17 is a side elevation view thereof;
  
    FIG. 18 is a top plan view thereof;
  
    FIG. 19 is a perspective view of an instrument showing a third embodiment of our new and ornamental design;
  
    FIG. 20 is an alternate perspective view thereof;
  
    FIG. 21 is an alternate perspective view thereof;
  
    FIG. 22 is an alternate perspective view thereof;
  
    FIG. 23 is a rear elevation view thereof;
  
    FIG. 24 is a front elevation view thereof;
  
    FIG. 25 is a side elevation view thereof;
  
    FIG. 26 is a side elevation view thereof; and,
  
    FIG. 27 is a top plan view thereof.
  The broken lines are for the purpose of illustrating portions of the instrument that form no part of the claimed design.