The aim of this series of four articles is to look critically, and in some detail, at the primary strategy approach to written calculation, as set out on pages 5 to 16 of the "Guidance paper" "Calculation." The underlying principle of that approach is that children should use mental methods whenever they are appropriate, whereas for calculations that they cannot do in their heads they should use an efficient written method accurately and with confidence. In the first part of this series, the author deconstructs the primary strategy's approach to written addition. The strategy's approach to addition is divided into four stages: (1) the empty number line; (2) partitioning; (3) expanded methods in columns; and (4) column methods. This progression matches the original National Numeracy Strategy (NNS) approach of counting [right arrow] mental [right arrow] jottings [right arrow] expanded written [right arrow] compact written, but unfortunately, like the NNS, shows a misunderstanding of the purpose of the empty number line (ENL). The Dutch, who developed the ENL, never envisaged it as a link between mental and written strategies, but rather as a tool to support mental calculation. It provides a physical, and then later, a mental model for such calculations. Here, the author critiques each stage of the strategy. (Contains 5 figures.)