One difference between Absorber 1 and Absorbers 2A/B which was not corrected is the difference in stack height. All three designs have a cylindrical stack, but 2A/B have significantly taller stacks. This difference is driven by uncertainty over stack requirements for continuous emission monitoring (CEMS), and does not represent an inherent difference between rectangular and round absorbers. However, there was insufficient detail in the cost estimates to adjust for the difference.