The article explores how estimating the substitution elasticity and TFP growth in economic models can be biased if technical progress is mis-specified. By analyzing a model consistent with balanced and near-balanced growth, the researchers found that the estimated substitution elasticity is lower than expected when using a factor-augmenting specification. They also discovered a non-negligible capital-augmenting component in the US economy's production function system, rejecting conventional neutrality forms. This study provides valuable insights into production and supply-side estimation in balanced-growth frameworks.