In CERES3 the following source code is used to simulate the influence of C02 on dry matter production DATA CO2X / 0, 220, 330, 440, 550, 660, 770, 880, 990,9999/ DATA CO2Y /0.00,0.81,1.00,1.03,1.06,1.10,1.13,1.16,1.18,1.25/ PCO2 = TABEX(CO2Y,CO2X,CO2,10) PCARB = PCARB*PCO2 Could someone please explain to me how this is calculated and what TABEX mean. Regards Andre