Hello there; In the program, there are two controls, manual and automatic, regarding the purchase of the reinforcement. In the form of defining the max and min reinforcement price when the manual control is entered into the relevant element parameters. For example, the default tension reinforcement purchase for beams is 0.003. However, in addition to this manually entered value, the program also calculates the "0.8*(fctd/fyd)" and "fctd/fyd" min price values required by the regulation and uses whichever is larger in the selection of reinforcement. Of course, it should be reminded that for the case of using the min pursantage in the selection of the reinforcement, if the required reinforcement is more due to the cross-section effects, the min reinforcement is not used and the calculated reinforcement is used. As for the situation you are facing, since I can't see your project, I make an estimation: First of all, since you used C16 concrete in your project, if we assume that this project is a reinforcement project and that S220 is used as reinforcing steel, the min purchase price for C20-S220 is 0.0044, while the min price for C16-S220 is 0.0039. therefore, there will be a decrease in the selected reinforcement depending on the concrete class. I am adding the explanation in the ide help on the subject below.