the numbers mean size of city (aka number of citizens), so whips from size 4 for 2 population points to size 2 and regrow back to size 4 gets best hammers return from all options.
I didn't do the calculations myself, but others did and said so... sooo I just trust them ;-).
granted some things can't be whipped in reasonable time for 2 population points, but at this phase of game maximizing outputs in particular cities is more for HoF players then for poor peops like me.
The early whip maximizing otoh is very important (you work with less cities) so it's worth remembering this calculations for the very few types of situations.
One thing that isn't (imo) implied clearly with the whip is that the saying about whips converting food to hammers can be seen in 2 different lights.
1) you get for population hammers and for getting population you need the food (thus the emphasis on high food cities and food being prioritized)
2) building settlers and workers and whipping THIS units into buildings brings you bigger hammers (except for situations with abundant mines and low food) then just plainly building buildings and whipping them, since all your surplus food (which is in early game abundant if you place your cities right) is used as hammers for producing settlers and workers.
there is one danger with OFing workers+settlers into wonders, especially in case of GLH which doesn't get any multipliers, that usually in your cap you should have enough pop and enough mines to get the GLH quicker without whipping and not losing the wonder (I had games where I went for OFing settlers+workers into GLH and losing that wonder, since the regrowth into mines was too long).
For this case is better to build settler before starting on GLH asap though, so you can run at least 1 city for supporting rex.
Btw Oracle usually is in the same boat since going for masonry for improving marble usually ends delaying you more then just going straight for Oracle and building it on mines + forests. It is never worth the wait for connecting marble, especially if you have marble in 2nd city.
Having marble in cap's BFC especially if you settle on it can be different beast and can be argued if masonry is worth it or not.
Thanks for the clarification, V!
Thanks for the thoughts on whipping settlers/workers, too! As a matter of fact, I am used to whipping them - as opposed to buildings -and was wondering if this might be one of the reasons for getting so much behind the AIs. Now, I think that this is definitely it, but not because of whipping those particular builds! It seems taht I was doing the whipping in a quite inefficient way: taking care of the penalty and the fast regrowth rather, than of the max OF.
BTW, as you see, I have taken your point on (civ) efficiency close to heart, and it has already helped in my side games, though not to the extent to win on Monarch yet... well, I also give up when I see that my chances are very slim, and my playing in the modern era might be a notch lower than in the initial eras, too.