When you need to add up a list of numbers, a calculator that prints a record of all the numbers you entered on a paper tape is useful because you can check the numbers one-by-one against the tape. If they all match, you're done. If you find an error, you can repair the problem without entering the whole list again.
A spreadsheet on your personal computer is the best solution. If an entry has a mistake, you can change it in the spreadsheet. When youre done, you can save and/or print the result.