Dear Hans,

Your sample works fine. This method gives me a flexibility of combining figures.

BTW, I have one question.

In the output, figure numbers started from 3, but suddenly jumped to 184. 
In a log file, 

metapost        > initializing number mode 'scaled'
floatblocks     > '3' placed
floatblocks     > '4' placed
floatblocks     > '5' placed
floatblocks     > '6' placed
floatblocks     > '7' placed
floatblocks     > '8' placed
floatblocks     > '9' placed
floatblocks     > '10' placed
floatblocks     > '11' placed
…
floatblocks     > '241' placed
floatblocks     > '242' placed
floatblocks     > '243' placed
backend         > xmp > using file '/Users/graph/ConTeXt/tex/texmf-context/tex/context/base/mkiv/lpdf-pdx.xml'
pages           > flushing realpage 1, userpage 1
pages           > flushing realpage 2, userpage 2
pages           > flushing realpage 3, userpage 3
pages           > flushing realpage 4, userpage 4
pages           > flushing realpage 5, userpage 5
pages           > flushing realpage 6, userpage 6
pages           > flushing realpage 7, userpage 7
pages           > flushing realpage 8, userpage 8
pages           > flushing realpage 9, userpage 9
pages           > flushing realpage 10, userpage 10
pages           > flushing realpage 11, userpage 11

I just curious why the number started from 3, and where are the numbers 4 - 182 omitted.
Is there any other meaning?

Thank you.

Best regards,

Dalyoung