You won’t find a dialog box in ƒ/Calc for changing preferences or other settings. Instead, ƒ/Calc just quietly saves all user interface settings and all the data values you give it. Every time something changes, it just saves it, no fuss. Because it recalculates all its outputs from its saved inputs at startup, ƒ/Calc always comes up in the same state you left it last.

I do it this way because it annoys me when a program makes me tell it something I already told it. Computers are good at remembering things.

During development, I’ve occasionally found it helpful to make ƒ/Calc forget all saved settings. Currently, it saves everything in a single file called a Local Shared Object, a mechanism of the Flash player. Flash stores these in different places depending on the operating system, so I’ll just point you to the article on Wikipedia about LSOs for more information. The ƒ/Calc LSO is called fcalc.sol. If you delete it (or disable LSOs altogether, as per the article) ƒ/Calc will start up with its defaults.

Regarding the security implications brought up in the Wikipedia article, be assured that ƒ/Calc only saves user interface settings in its LSO, and the data stored in it never gets sent up to fcalc.net. ƒ/Calc will still work if you disable LSOs in your Flash player; it’ll just forget everything you tell it when you go to another web page.