If you bind off at the end of the row too it will leave your working yarnin the wrong place to be able to carry on without breaking it and re-attatching it again. Instead you bind off at the start of a row work to the end turn bind off again and the work the rest of the row. It does meen that the shapping for one side starts a row after the other side but it is a small enough difference that it doesnt realy show or alter the look fo the finished piece.
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