The ornamental design for an accessory for weighinginstrument, as shown.
FIG. 1 is a top perspective view of the accessory for weighing instrument;
FIG. 2 is a bottom perspective view thereof;
FIG. 3 is a top plan view thereof, the intersecting broken lines illustrating two co-planar axes of symmetry;
FIG. 4 is a bottom plan view thereof, also showing the axes of symmetry;
FIG. 5 is a side elevation view thereof, along either of the two co-planar axes of symmetry, with a third axis of symmetry, normal to the first two axes, shown in broken lines; and,
FIG. 6 is a top perspective view thereof, in operative position on a weighing instrument, which is shown in broken lining as unclaimed environmental subject matter.