the first and second accumulator shelves 128 134 the controller extends the first and second accumulator shelves 128 134 and the receiving conveyor 26 moves the finished stack away from the frame 102 of the buffer apparatus 100 the first rollers 130 and the second rollers 136 continue to operate to support sheets exiting the digital printer and to drop them individually onto the stack forming on the first and second accumulator shelves 128 134 when the receiving conveyor 26 is back in position and ready to receive more sheets the controller retracts the accumulator shelves 128 134 and drops the accumulated sheets onto the receiving conveyor and the process of receiving sheets on the first and second rollers 130 136 continues as before until the new stack on the receiving conveyor has reached a desired height the buffer apparatus 100 described above can also beneficially be used to stack sheets that are relatively short that is sheets short enough that they do not droop and drag along the top surface of lower sheets in a stack specifically as discussed in greater detail below the side tamping plates 142 144 can beneficially be used to tamp and square sheets of a stack on the receiving conveyor 26 as well as to tamp and square sheets that are located on the accumulator shelves 128.