Hi Yichen
i'll give you my version of CBM with an example.
Steps 1-2-3 of a reverse turn in the slow waltz. A beginner would probably dance this: Right foot back on 1 (these are lady's steps). Rotate left by 120 degrees (3/8 of a turn) and left to side on 2. Close Right to left on 3.
A more advanced dancer would be thinking of turning all the time, not just on step 2. Thus the same steps would be:
right foot back, softening left leg and rotating upper body to left (for a reverse turn). This body rotation starts as the right leg is moved back, so that, as the right foot is planted (in its final spot, as it were) the upper bosy has rotated 45 degrees (1/8 turn) approx. At this instant, you are in CBMP (i think), but in any case, you're in the middle of a CBM. Your left leg hasn't yet moved, the right leg has moved back along its line. but your upper body has rotated, leaving your left shoulder towards the right (moving )foot. This is why the books say that the opposite shoulder moves towards the moving foot.
In all dances involving turns, CBM is inevitable if the turning action is to be continuous throughout the turn, as it is for a reverse (or indeed natural) turn in a waltz.
Try it - you'll get the hang of it. However - as a lady, you MUST follow your partner. If he doesn't put in the CBM, it'll be difficult for you to do it.

It's interesting you mention this passing through CBMP in an ordinary CBM action. I think this is very nearly what a lot of the top English teachers do and request, wanting the body turn nearly complete by the time the foot is placed for the first step, but good luck finding any American coach who will agree with or do it.

Only thing I would change is to talk about rotation in the hips rather than the upper body. It's hip rotation that will make or break a step. I think a reverse action is primarily in the hips first and top only later, but even if you think they occur together it is probably good to concentrate on the hips and not the top - otherwise you usually get shoulder rotation and square hips. When the book says body, what it specifically means is hips - this makes all the descriptions (promenade for example) much more clear.

Good explanation. Thanks.
When I rotated my upper body more than before I did , the steps became fruently .

Just a quick clarification. CBMP means placing the moving foot on the track of the standing foot without resorting to body turn to do so. You can still have body turn coinciding with CBMP, but the turn is not what creates the CBMP position . At least in the swing dances, CBMP has to come as a result of a trajectory established on a previous step, you can't create it at the moment that it occurs. Natural turn outside partner in quickstep - there is CBMP as a result of how the previous figure ended, but there is also body turn - CBM - to make it a natural turn.

In tango the establishment of CBMP is a bit more complicated... in fact it appears we often do turn the body and step into CBMP. Perhaps the term CBMP is misapplied to tango... mostly it is just a very strong CBM. Or perhaps the hint is that we are supposed to turn the body in tango while in place over the standing leg, and then move in a straight direction. That would mean the turn that causes CBMP is preceding the action of stepping as in the swing dances, even though it is happening during the time alloted to the step where it results.

Recently, I have stronger impression of that dance should be easy and smooth. The foot work , the body rotation and the technique developed serve this purpose. Spotdance is a dance that 2 bodies dance as one unit. We design moving forward , backward, sideward, turning to enable the dance attractive . When we move laterally ( outside partner and maintain connection as well.) CBM ( turn standing side body toward free leg ) and CBMP ( footwork , one track or more than one track ( freet foot cross the standing foot a little bit) needed or occurred inevitably to serve the purpose mentioned.
Feather step on 4, shoulder leading is maintaing, so just put the free foot cross it without body turn, CBMP.
Here, it is established after 2 and 3 step. We have enough space to simply put the foot in progress ( feather step ).
More compact body connection may need stronger CBM and has a consequence of CBMP in side moving. such as 5 steps in tango. Correct me , if I was wrong. Thanks.

I think you mean step 3 of the feather - this is the step that achieves CBMP for otuside partner by keeping the same side in advance that was leading in step 2.

Step 4 usually features CBM to initiate a following reverse figure of some variety. While reverse CBM is felt more in the hips than shoulders (at least compared to natural CBM), it will still have the effect of changing which side of the body is leading.

CBMP means to step the foot across the body. In Tango the man has a strong left side lead so he does not have to turn his body to dance cbmp with his right foot. In the feather step in the foxtrot we use cbm(swing) to turn our body(side) so that we can step outside our partner from knee to toe only,while keeping our hips in line with our partner.

Actually tango is danced with a RIGHT side lead - you move towards your right side, it gets there first, so it is leading (check the figure descriptions). However, the normal leftward stretch must be maintained, and the two concepts are often confused.

See also the three step in foxtrot.

Sorry I should have said right side left leg,we curve to the left. I remember practicing the walks around a chair. The good old days.

CBMP is simply the abbreviation of'Count Body Movemnet Position'
It implies your current walking (both forward or backward) maintain a postion whereby the right hand swings forward while walking forward with your left foot and keeping your upper body slightlt swinging towards towards the left (or the left hand swings forward while walking forward with your right foot and keeping your upper body swinging slightly towards the right)
This movement position if often seen while a troop of scouts is 'marching' down the sports field. In the ballroom it is often seen while a couple is dancing the slow fox-trot.