I'm the introduction, the situations that should require the use of a calculator are?

When you are unavailable to work in your head, for instance 1+1=2 No need for a calculator as that is a no brainier, now try $12,001,615,817.99 subtract a sum amount of $2,278,726.71 and then multiply by 12,000.

all math past 6th grade.

Step-by-step explanation:

that's when math starts to get really difficult and the process of "showing work" takes too long nowadays, so teachers schools etc even students buy calculators.