Knitting woes

After finishing all the pieces and sewing the sleeves togehter I noticed that one of them was 6 cm longer than the other one. I have no idea how that happened, but I have now unpicked parts of the under arm seam, cut off a piece (I had fastened all the threads so it wasn't easy to unpick), unravelled a lot more and started knitting a new sleeve head. I ought to have finished the cardigan when I go to Uppsala on Thursday morning for a meeting about fashion history courses.