Thank you very much, Latindancer. You have solved my problem : standing on Both balls. and standing Heel finally flat gradually.
ylchen

Yichen. A Spiral to the left. Make sure you put all your weight to the LF then the RF. then Spiral on the spot. Check that you are upright and stretching your spine. Even the slightest wobble will throw you out.

Thanks for good advice.
I am still searching the musical phrasing.
Now I made clear the difference of CPB ( locates in top of central zone. where cross line from shoulder to opposit hip )and Center of body mass ( 2 inches above umbilicus )...
ylchen

Anyone who has Slavik's DVD on Cha Cha will know all about stretching the spine which is essential for Latin and equally so for Modern. He demonstrates the wrong way and the correct way. Untill I saw this I always thought that I was using my spine correctly. Look in a mirror and separate the ribcage from the hips. You will soon find out if your upper body has been sitting on the lower part even though the back is straight. To do a Spiral correctly ,the above is of prime importance.