How should I markup units of measurement in HTML5? (Centimetre, grams, etc.)

[dbvatos]

I markup a table which contains values with units of measurement.I thought about how to mark up the HTML for the best accesibility.Is it important to respect changing values and constant names for values?I did not find any \[code\]<value>\[/code\], \[code\]<unit>\[/code\] element or an appropriate attribute for this case.My three markup approachs\[code\]<table> <td>Brain weight</td> <td>3.8<em>g</em></td></table>\[/code\]