Measurement Microformat

Is anyone doing anything with measurement units in microformats? If not, here's a RFC. I'm thinking something like this would be a good place to start:

<span class="mm">73</span> mm.
<span class="in">24</span> in.
<span class="oz">96</span> oz.
<span class="m">3.2</span> m.
there are <span class="ft">5284</span> feet in <span class="mi">1</span> mile.

And so on. What do people think?