Rejewski states that writing down all the possible "would be too laborious", so he developed the grill (grid) method. "Next, the grid is moved along the paper on which the drum connections are written until it hits upon a position where some similarities show up among the several expression . ... In this way the setting of drum and the changes resulting from permutation are found simultaneously. This process requires considerable concentration since the similarities I mentioned do not always manifest themselves distinctly and can be very easily overlooked." The reference does not describe what techniques were used. Rejewski did state that the grill method required unsteckered pairs of letters.