I don't think there are any rules. Its a simply reality that...

I don't think there are any rules. Its a simply reality that whenever a security is traded on multiple exchanges it gives rise to arbitrage opportunities. Market cap, logically, should be calculated on the prices at the bourse with the greatest volume.

The puzzle to me is how stock has become available for trading in Frankfurt. Like, the major shareholders and staff surely wouldn't be sellers. So does that mean a German stock broker has-bought/is-buying stock on market in Australia to later sell in Frankfurt?!!

Gimme Migme