What's the best way for the number roller to input the final value into a field?
With an API call I would think. Assuming the record is either already created or you need to create a new one straight from the code page.
So what is the ultimate goal here? For it to be contained on a form, or are you okay with the code page? You want this to receive multiple inputs from where?
Usually the way you would use a code page is to send data to it in the URL via a button or some other method. Then in your code page you parse the URL for the data you sent and do what you need to do in the code page then make an API call back to where you want to be with the data.