I spent a week in Stockholm recently. At Arlanda, I bought a 7-day SL card as my best option and used it on public transport to get into town. Now I am looking at my receipts and see I was charged 260 SEK for the SL card and another 20 SEK for "kortforsaljning" (fill in the diacriticals). I see this means "short sales"? Was I charged for something I should not have been?
I also found out later that since I arrived Thursday evening and used my SL card that night, I lost an entire day on my SL card. This doesn't seem quite right, so travelers should understand that you use a day no matter when you first start using the card.