If you have voted form your computer (IP) than if you will try to vote again it will say that you have already voted + you wont receive credits.
And if you go to other side of your country and try to vote from other computer(IP) I think it still wont give you credits because it's the same account.
It have been made to don't allow people do that and get multiple time's VOTING CREDIT REWARD.
And it's made to make it harder to get credits of voting, because people can change they're IP addres and VOTE again from the same account = no CREDIT REWARD.
Hope this gave you full information.