First visit? Your browser is downloading R and the packages PowerR needs (≈ 50 MB total) so the simulations can run entirely on your machine via WebAssembly.
This typically takes 15–30 seconds on a fast connection. Subsequent visits start almost instantly from your browser's cache. Nothing you enter is sent to a server.
Stuck for more than a minute? Check your network connection, or run PowerR locally — see the Tutorial tab once the app loads.