In the cases with capital A's, you can tell by the spacing between the two "legs...

		67726e on Jan 20, 2013 \| parent \| context \| favorite \| on: So you think you can tell Arial from Helvetica? In the cases with capital A's, you can tell by the spacing between the two "legs" of the `A`. Helvetica is more compact. The space inside `O` is more compact for Helvetica as well.