<qa>  What is the position of the breast fixed in the compression device?A stereoscopic digital mammogram consists of two x-ray images of the breast acquired from slightly different points of view on a digital mammography unit. The x-ray source is rotated 10-degrees between the two exposures while the position of the breast remains fixed in the compression device. The stereo pair of mammograms is viewed on a new third-generation, high-resolution stereo display workstation that was developed in the first part of this project. The mammographer views the stereo display wearing lightweight polarized glasses, enabling him or her to see in depth the internal structure within the breast. As a result, a subtle lesion that may be obscured by superimposed normal tissue in a standard 2D image, now becomes visible as the overlying and underlying normal tissue is separated in depth. Conversely, layers of tissue that may falsely resemble a lesion in a standard 2D image due to chance superimposition, are seen in the stereo mammogram to lie at different depths and, thus, will not be mistaken as a lesion. 