Under the "Limitations" section:

> Range is always a normal distribution, with the lower number being two standard deviations below the mean, and the upper number two standard deviations above. Nothing fancier is possible, in terms of input probability distributions.

Part of the confusion here is likely that the tool, as seen on the web, probably lags significantly behind the code. I've started using a related but different tool (https://filiph.github.io/napkin/).

The HN mods gave me an opportunity to resubmit the link, so I did. If I had more time, I'd have also upgraded the tool to the latest version and fix the wording. But unfortunately, I didn't find the time to do this.

Apologies for the confusion!