JavaScript Birth Date Calculator

Modern tombstones inscriptions typically give both the date of birth and date of death. Older tombstones are more likely to give the date of death and persons age, such as:

So what date was John Doe born? Obviously it's not a trivial calculation!

I've written a JavaScript that does such calculations for the old tombstones. To start it, click on the Calculator button above. (Browser support for both frames and JavaScript is required.)