The document discusses errors in using the intercellular CO2 concentration (Ci) parameter to model photosynthesis. It provides evidence that CO2 diffuses uniformly through leaves, not just through stomata, as commonly assumed. This decouples photosynthesis from transpiration. It also notes the Ci scale points are inconsistent between plants, making comparisons unclear. For accurate comparison, it suggests using the external CO2 concentration on the x-axis of charts.