Private methods in a module, and modules in BangleApps

Good plan - I'm not sure s1 gets set up? You could actually do:

let s1 = (n&1)?1:-1, s2 = (n&2)?1:-1;

and remove the whole switch

I've just updated the app loader to allow local modules for you: https://github.com/espruino/BangleApps#modules

So add the module in modules/, then reference it from your code as just require("mymodule") and you should be good.