Everything starts from limits. You have to know your limits. This is a new way of thinking. Riemann may have beaten Newton to the punch on this, but Newton's was the first published theory. Calculators Calculators are not good at mathematics.
Calculators are great at giving numbers to ten or twelve significant digits.
You can't trust your calculator to give you the umpteenth digit - it can't, and it won't. Calculators have batteries which eventually run out. You have a brain doesn't need batteries.