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| This used to be my ATMs.... |
Just like in Argentina, when they froze their currency, the first thing that will happens is that the ATMs will shut down. Not due to a run on the banks or anything, but just because the software hasn't been designed to go backwards. Actually it was - in the very very beginning of the Euro - in case the whole thing didn't work out, but that was dropped after a few months.
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So there is no process in place to change this. The easiest quick fix is to add Drachma's as a secondary currency - and show the conversion rate to the home currency. Some countries already do this (where you can withdraw Dollars or local currency). Now, while this will work, it is annoying as this shows how much money you lose everytime you withdraw Drachmas. And, until they write new software, it will continue to say, "I'M SORRY, I DON'T HAVE EUROS, DO YOU WANT DRACHMA?" Because it is the (expected) base currency that is out of (ie not loaded).
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Whether from CIT or out outside company, changing a base home currency is a process that normally takes months, if not years. As a matter of fact, it isn't done. The Euro was a first. A huge, 3 year planned first.
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It won't be pretty. And it will look even uglier. And, as in Argentina, expect a bunch of riots / attacks on ATMs and banks.