What is the meaning of W and T symbols on the depth of field scale?

W indicates wide focal length and T indicates telephoto. For example on a 28-80mm zoom lens W is equal to 28mm and T is corresponding to 80mm. Depth of field region can be determined by combination of depth of field scale and distance scale. The depth of field scale is printed on depth of field scales on the right and left sides of the centre index line. These figures show the depth of field for each aperture setting. The range between numbers of the same f-number is the depth of field. For instance, choose the aperture, f22 and rotate the zoom control to the wide position until it stops and focus the lens on a subject. The distance from the camera to the subject will be shown on the distance scale by the centre index line. Therefore, the region between the right and left sides of the centre index, which will be in the range of the same f-number at the chosen aperture, will be in-focus. The same process also can be applied for tele-position. Set the focal length to tele-position, choose the aperture, f22. You would see the range on the distance scale, which corresponds to the depth of field.