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