How to do arithmetic and [some] algebra.

Calculator/SW    vs.   hand
--non-baby numbers     123.456*543.67
--important   e.g. personal finance, IRS, business, project/research
--many  

Calculator     vs.   SW/CAS
--[more digits]      --looks like the math
--no Internet        --editable, then re-do
                     --Algebra
                     --excellent graphs