By convention, when a projection of glyceraldehyde is arranged with C-1 at the top, the stereoisomer in which the OH group at the chiral center projects forward and to the right is called D-glyceraldehyde. The mirror image is called L-glyceraldehyde. This convention has been extended to other carbohydrates. There is no correlation between D and L and (+) and (-). Thus D-glyceraldehyde is dextrorotatory, while D-threose is levorotatory. There are four D-aldopentoses; three are levorotatory and one is dextrorotatory. There are eight D-aldohexoses; six are dextrorotatory and two are levorotatory.