How can I get two calculators going?
The quickest, simplest and arguably most correct way of doing this is using the open command in Terminal.

In a new window, run the command 

open -na Calculator


This will open a new (-n) instance of the application (-a) Calculator.

If you want to have this handy at the click of a button, you can type the following commands into the Terminal, and it will create a shortcut named calc or calc.command on your desktop that will always open a new instance of Calculator

cd ~/Desktop
echo open -na Calculator &gt; calc.command
chmod +x calc.command
exit


Mind that you don't already have a file named calc.command on your desktop, or it'll be deleted!