The first step in creating a customizable Focused Calculator is to choose an existing calculator that is similar to the calculator you want to customize.
From the calculator list, slowly "left swipe" the row of the calculator to display the row actions. Then choose "New Child".
A new calculator will appear in the list with the same name of the parent calculator with "child" appended to the name and an asterisk before the name. The asterisk indicated the calculator is not "read only".
You can now tap the detailed information button i is to display the Calculator Editor for that calculator.
Or, you can select the new calculator and "Paste Keys".
CALC 1 Focused Calculators use a form of Inheritance from object-oriented programming.
The keys on the child calculator "override" the keys of the parent calculator.
So when you create a new child calculator the new calculator will have no keys assigned and the editor will show all blank keys.
This makes it easier to create new custom calculators since the custom calculator only needs to have the keys that are different from the parent calculator. Then if the parent calculator is updated, the child calculator gets the updated keys.