You should execute input function blocks before you execute output function blocks, or your performance could suffer. If you created your output function blocks first on the diagram, you will want to change the default execution order.
Hold down the CTRL key, and then click a block to define it as the new first position block.
Hold down the SHIFT key and click a block to indicate that you want the next block you click to be the next block in the execution order. Using this feature, you do not have to start at the beginning and set the order; instead, click the last block in the order that is correct while holding down the SHIFT key, and then continue clicking the next blocks in the desired order.