First of all, thanks for the explanations. I wasn't confused at all, that's why I asked again for confirmation/explanation. As it shows, your last post is on another topic, maybe your previous formula was too, so apologies if I read it as the wrong thing.

However, the rather simple and maths proven stuff on determining the TOD and the descent rate necessary to achieve and maintain a 3 degree path may, for example, be well summarized here. http://selair.selkirk.ca/Training/misc/math/get_down.html
As some simple graphics got added too, I hope that the confused guys now can get back to more stable regimes while enjoying the extra reads on other topics from your side.  :)

Here's one on the approach portion. http://www.navfltsm.addr.com/gs.htm

As a side note. The FMC equipped and 'VNAV' able birds don't calculate their stuff that simple of course. Their advantage comes from calculating optimal values in regard to the current conditions, which for instance takes ISA deviations into account.
That's the reason behind the data entries on the descent page by the way. The winds and the planning for when anti-ice is on are vital when it comes to planning an optimal descent path, taking the higher idle from anti-ice stuff into account for example.

The same goes for the winds. They affect groundspeed (GS) and therefore alter the descent angle if being left uncorrected. Which then leads us back to the simple dependency of the vertical speed (VS) needed in regard to the groundspeed (GS) of the plane. Otherwise you under- or overshoot your end of descent point because you've left the pre-planned path.

So either have a smart FE on board or an even faster VNAV computer, getting the right source data from his pilots. Last step is mandatory, at least in the rw.