SUB is for subscripts


The "sub" element is for treating a character as a subscript, displaying it in a smaller text than its surrounding text, and lowering its typographic baseline.


decimal         1000dec          1000<<sub dec>>    

hexadecimal 400hex 400<<sub hex>>

binary 10000000000bin 10000000000<<sub bin>>

glucose C6H12O6 C<<sub 6>>H<<sub 12>>O<<sub 6>>

one-thousandth 1/1000 <<sup 1>>/<<sub 1000>>

care of c/o <<sup c>>/<<sub o>>
The sub element

semantax > term-mark > subSUB is for subscripts