Each row is a day an official rate moved 10% or more. The gap is how much more a dollar cost on exchanges than at the official rate.
From exchange history, not our own hourly checks.
The gap before is the typical exchange price in the second week before the jump against the official rate. The gap after is how much of it was still open once the new official rate settled, in the third week. A blank means we have no exchange price for that time.