Ask HN: How to determine equal pay for genders at a company?

I have a question sparked by the NYT Gender Equality link on the main board as well as a throw away comment by a former co-worker yesterday.

With a few women at my past work, I've had the discussion about equal pay for experience and, since the majority of payroll is opaque, the general assumption is that they get paid less, even though that workplace claimed to be "very progressive".

The general assumption for pay was that it was whatever you were able to negotiate when you came in.

Beyond that though, how would you figure out if a company actually was or was not paying people equally for equal amount of experience, regardless of gender?

I guess the easiest answer would be to have enough trust and honesty with some of your co-workers that you could freely discuss it. Since I was not in the same profession as them, I had no trouble discussing my salary but, especially in the US, it's seen as something that's not done.

I don't think this previous company were consciously nefarious, only that the operated like a company does, getting people to work for as little as they'll accept.

Curious what others think.