The chapter discusses the arrangement of field experiments in agriculture, focusing on the precision and validity of error estimates. The author, R. A. Fisher, highlights the importance of distinguishing between errors that can be eliminated and those that cannot, and emphasizes the need for a random arrangement of plots to ensure valid error estimates. Fisher explains that a valid estimate of error is crucial for determining the significance of experimental results, and he outlines methods such as replication and randomized blocks to achieve this. He also introduces the concept of the Latin Square, a systematic arrangement that maximizes the elimination of soil heterogeneity while providing a valid estimate of residual errors. Fisher argues that complex experiments, which involve multiple factors and comparisons, are more efficient than simple ones, as they allow for a broader range of questions to be answered with high accuracy. The chapter concludes with a discussion on the practical implementation of these methods and the importance of careful design and reporting in field experiments.The chapter discusses the arrangement of field experiments in agriculture, focusing on the precision and validity of error estimates. The author, R. A. Fisher, highlights the importance of distinguishing between errors that can be eliminated and those that cannot, and emphasizes the need for a random arrangement of plots to ensure valid error estimates. Fisher explains that a valid estimate of error is crucial for determining the significance of experimental results, and he outlines methods such as replication and randomized blocks to achieve this. He also introduces the concept of the Latin Square, a systematic arrangement that maximizes the elimination of soil heterogeneity while providing a valid estimate of residual errors. Fisher argues that complex experiments, which involve multiple factors and comparisons, are more efficient than simple ones, as they allow for a broader range of questions to be answered with high accuracy. The chapter concludes with a discussion on the practical implementation of these methods and the importance of careful design and reporting in field experiments.