The ornamental design for a monitor, as shown and described.
1. Monitor
1.1 : Perspective
1.2 : Front
1.3 : Back
1.4 : Left
1.5 : Right
1.6 : Top
1.7 : Bottom
1.8 : Partial enlarged perspective
Reproduction 1.8 is an enlarged view showing a portion of the control box at the bottom of the display panel; the oblique shading lines in reproductions 1.1, 1.2 and 1.8 are used to show the display screen of the claimed design, and do not represent its surface ornamentation.
The dash-dash broken lines depicting portions of the monitor represent features that form no part of the claimed design. The dot-dot-dash broken lines forming a rectangle in reproduction 1.8 are included for the purpose of illustrating the partial enlargement and form no part of the claimed design.