The auto TSO only works on linear array transducers on the Canon systems currently. If you do not have auto TSO use a higher number for dense or lactating breasts (+2) and use a lower lumber for fatty involuted breasts (-6). This is a good guide, but feel free to experiment. Remember TSO is also active when you are performing MSK, obstetric, abdominal examinations etc and you can use the same theory of higher numbers for low BMI individuals and a lower number for high BMI individuals.
Steve