You are offline
The page you asked for has not been opened on this device before, so there is no copy stored here to show you. Anything you have visited already will still work.
What still works without a connection
Every page you have opened before, and every calculator on them. All of Lookmetry's arithmetic runs on your device — the pupillary distance maths, the lens thickness figures, the colour conversions — so none of it needs the network once the page itself has loaded.
The camera tools are the exception, and only on a device that has not used them yet. They need the face model, which is a few megabytes and is fetched the first time you open one. After that it is stored here too and they work offline like everything else.
Nothing you measured has been lost
Measurements are kept on this device rather than on a server, so a dropped connection cannot take them with it. They will be waiting when you reconnect.