Willie Rennie has challenged the First Minister over his plans for a currency transition period.
Alex Salmond has said keeping the pound without the Bank of England’s support would only be a stopgap.
The Scottish Liberal Democrat leader is now calling for "clear details" of the proposed "transition option."
In theory, this would see Scotland continuing to use sterling even if the UK parties continue to reject a Eurozone-style currency union.
Mr Rennie believes uncertainty will be the Yes Campaign's undoing.
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