Although it looks like a calculator, the contents are a browser app

The icon displayed on the home screen looks like a calculator, and the calculator will be displayed first when it starts up.  It can also be used as a real calculator.  Enter the password into the calculator in a special way and the browser mode will be activated.  This browser is a dedicated browser in the app, not Safari.  You cannot access your browsing history or bookmarks from other apps.

Returns to the calculator mode automatically

Browser mode is automatically terminated when you leave the app by pressing the home button.
The next time you open the app, you will return to the calculator screen, but if you enter your PIN, you can resume browser mode.

Point more convenient than Safari and Chrome

The advantage of the private browse mode that is included in general browsers is that no history is left, but there are many browsers that cannot be locked with a password.  Some people may delete tabs every time after using private browse mode.
However, Calculator-R has a lock function, and the lock itself is hard to understand.
This is ideal, if you want to save a bookmark or keep a history, but also want to avoid knowing that it is locked.