An indicator configured to be attached to a wound dressing includes first and second parts. The wound dressing is configured to collapse in response to an applied negative pressure. The first and second indicator parts are configured to move relative to one another as the wound dressing is collapsed. The movement of the first and second indicator parts is configured to allow a user to easily visualize the compression of the wound dressing and monitor the application of the negative pressure to the wound dressing. A marker is provided along a top surface of the first part and a window is formed on the second part. The changes in the portion of the marker that is visible in the window as the first part is slid into or under the second part are configured to provide for easier detection of the collapse of the wound dressing by the user.