The ornamental design for a diagnosticinstrument, as shown and described.
FIG. 1 is a perspective view of the diagnostic instrument;
FIG. 2 is an enlarged view of a portion of the diagnostic instrument shown in FIG. 1;
FIG. 3 is a top view of the diagnostic instrument;
FIG. 4 is a bottom view of the diagnostic instrument;
FIG. 5 is a first side view of the diagnostic instrument;
FIG. 6 is a second side view of the diagnostic instrument;
FIG. 7 is a first end view of the diagnostic instrument; and,
FIG. 8 is a second side view of the diagnostic instrument.
The broken lines in the drawing views are included for the purpose of illustrating portions of the diagnostic instrument that form no part of the claimed design.