I normally use a small local html file.
Attached is something I put together for your calculator.
Change the extension from .txt to .html and open it with a browser. I got better results with Firefox. Chrome adds too much extra space around the web page.
It does an auto-calculation on key strokes but since I didn't know the actual formula I multiplied all values together. On every user input it should auto-calculate.
In order to change the formula open the file with a text editor and change the line with what you want the output to be:
var output = acctSize * trRisk * slTicks * tickVal * noContract;
You should get something like the picture below:
View attachment 251540