Final answer:
In Excel, the tool button used to sum a large range of data is called 'Sum'. This function allows for a quick total calculation of selected cells.
Step-by-step explanation:
In Excel, you can sum a large range of data by simply selecting the tool button called Sum. This button is typically represented by the Greek letter Sigma (Σ) and is found in the 'Home' tab of Excel in the 'Editing' group. When you click this button after selecting a range of cells, Excel will automatically calculate the total sum of the numerical values in that range.