For the AutoSum icon itself, you would need to add it to the Quick Access
Toolbar. Right-click the QAT and choose Customize... Set Choose Commands
from: to Commands not in the ribbon. Scroll down to the S's and find Sum,
then click Add.
The sum feature can also be found by clicking the Formula tool in the Data
section of the Table Tools - Layout ribbon tab (along with other field-based
formulas that are supported, such as ABS, AVERAGE, COUNT, PRODUCT, etc.).
