[NTG-context] Part number in formula numbers?

Hello, what I'm trying to achieve is a way to have formula numbers contain the part number together with the chapter number, as in: a = b (part.chapter.formula) instead of a = b (chapter.formula) which is what you have by default, or a = b (part.formula) which is the only alternative I manage to obtain. How can I do it? -- Giuseppe "Oblomov" Bilotta