Decorate cake. Prepare buttercream icing following recipe directions. Tint light blue. Use spatula and blue icing to ice cake smooth.
Use cake dividing chart to divide cake into 10ths. Mark at bottom with toothpick. Use cake marker to mark 1 in. divisions from bottom mark to top on cake sides. Mark the center top of the cake. Use toothpick and ruler to mark three 1 in. divisions on top of cake from center to edge of cake.
Use tip 5 and blue icing to pipe drop strings between divisions marked on sides. Use tip 5 and blue icing to pipe scallops between division marks on cake top as well as to pipe large center dot. Pipe tip 5 dots at all points on cake sides and top.