Online usage, no download necessary: Fill out the form at https://ukyuav.github.io/hab_fill_calc/ Hover over the question mark icon for each calculated field to see an explaination.
Offline usage: Download both calc.js and index.html to the same folder. From the file manager, right-click on index.html and open in a browser. The fancy spacing and button styles are provided by Bootstrap which is loaded by a CDN and are only available with an internet connection.