A clinical instrument typically used by a surgeon during breast reconstruction surgery consultation and/or preoperative planning as a guide to select an appropriately-sized breast implant (mammary prosthesis) and tissue expander. It is typically a transparent anatomical template used with other devices (e.g., calliper, measuring tape) to measure various dimensions of the patient's existing breast (e.g., width, height, projection) for selection of the optimal expander/prosthesis to achieve symmetry with reconstruction. The device is provided in a range of dimensions. This is a reusable device.