Plywood grades are (best to worst) A, B, C and D for face or front face. The back grades are (best to worst) 1, 2, 3, and 4. Plywood grades of A1, A2, B1, B2 are a good two-sided product and would be used where both sides are going to be seen. The backside (number grade) does have a few more blemishes than the front. A3, B3, C3 are for plywood that will be seen from one side, but the backside must be clean, although there may be some stain or discoloration on the back, spliced veneer, and so on. One might use this material for the sides of a dresser (who looks inside?), for drawer sides, and shelving. A4, B4, C4 are a one-side-good product. The back may have open knots, filled knots, bad veneer joints or seams. This material will work well for drawer bottoms, and similar.