Why won't Calculator convert currencies and units?

Y'know, for a company that prides itself on making brilliant interfaces, there are occasionally glitches and very poor interface elements that creep out of Apple's offices in Cupertino and that we're then stuck with for far longer than seems necessary.

Though a humble application, the Mac OS X Calculator has just such an interface glitch and that's what you've bumped into, hence your question. I've seen it too and puzzled over the problem so I know what's going on and how to fix it.

In fact, there's nothing to fix. In fact, Calculator is working exactly as it's supposed to with the grayed out menu options.

Here's the problem:

Frustrating as heck and, in a classic user interface problem, there's no indication of why everything's grayed out.

So here's the secret: you can only choose from the options on the Convert menu once you've entered a non-zero value in the Calculator itself.

Really. Try it. Enter any value in the Calculator and suddenly the menu changes to:

So now you know too.

Memo to Apple: this is stupid. Fix it, please, or at least have all the Convert options pop up a small window that says "Usage: enter a value into the Calculator, then choose a Convert option."