Wiki for a better world:Calculator/Known bugs
When you're editing & previewing a section of a page, if your calculation depends on a datapoint from a previous section, it'll get an "Unknown unit" error. But when you hit 'save page', the error will disappear - the actual page should show the calculation properly. Tip: edit a big enough section of the page that you can test/preview your calculation without this error.
When declaring datapoints that depend on other datapoints, the order matters. If you reference a datapoint that isn't declared earlier, you'll get an "Unknown unit" error.