The ornamental design for a demonstrationdevice, as shown and described.
FIG. 1 is a front perspective view of a demonstration device showing our new design;
FIG. 2 is a rear perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a right side view thereof;
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom view thereof.
The broken lines shown in the interior of the rectangular area of the chute portion of the demonstration device shown in FIG. 7 are included for the purpose of illustrating a portion of the demonstration device that forms no part of the claimed design.