Variable length list input

I'm writing a wasm statistical calculator, so I need to allow an arbitrarily long number input on my website's front end. My current design looks like this:

A number is entered where the line is. Enter adds a new number input to the end and focuses it. Emptying an input removes it (and similarly focuses the last element), for instance like below:

The 'calculate' button can be clicked/pressed, and the page logic will take place, outputting results above the input.

How can I improve this such that it takes no instruction to use?