The article explains how it takes time to build new capital goods, like ships and factories, which affects economic fluctuations. By using a modified equilibrium growth model, the researchers found that the assumption of multiple-period construction is crucial for understanding these fluctuations. The model, fitted to U.S. data, shows that finished capital goods, not half-finished ones, contribute to the productive capital stock. The model also considers the importance of leisure in addition to consumption for households, and incorporates shocks to technology and productivity indicators. Overall, the model provides a good fit to the data and integrates growth and business cycle theories.