They (I'm swiss, so I wasn't affected that much by the transition) had a double display (prices in french francs/ deutschmark / lira) for quite some time before

They (I'm swiss, so I wasn't affected that much by the transition) had a double display (prices in french francs/ deutschmark / lira) for quite some time before and after the introduction of the actual currency (coins and banknotes). It's not a perfect solution, of course, but the point is that the transition wasn't abrupt.