How the depth is measured?
In general the illusion of depth is created by slightly displacing the objects in horizontal direction. Later in this manual this is recalled as "parallax". If you move the object of interest in the left picture to the left and in the right picture to the right you will create an illusion that the object is moving inside the screen. And vice verse, if you move it in the opposite direction you will create an illusion that the object is reaching out of the screen.
In 3DTitles the monitor surface is assumed to be the zero point. If the subtitle is placed inside the monitor it has positive depth, if it is outside the monitor the depth is considered to be negative.
There is no absolute way to measure the depth. It depends on many factors including the distance between the human eyes, viewer's distance to the screen, screen's size and resolution, etc. In 3DTitles it is measured in units representing the monitor (screen) width. A depth +1.0 means that the object is placed one monitor width inside.