Problems calculating field in model builder

Discussion created by grastafaram on Mar 14, 2012
Latest reply on Mar 16, 2012 by grastafaram
Hello, I am attempting to build a model that adds a new field to an attribute table, lets call it New_Temperature,  and then calculates a value for that field by adding a value, determined by the user, to the original Temperature field.  For example, I would like to create a new field that is 7 degrees more that the original field.  I have included a screen shot of the model that I attempted to build.  Plots is the .shp file with the attribute table.  I got the first step to work, where the model adds a new field, but I get a warning saying that "The process did not execute because the precondition is false." 

I am pretty new to this, so I'm not sure I specified everything correctly.  In the Calculate Temperature box I put "[Tma_ºC_] + %Temperature Change%" for the expression field, so I assume that means the Calculate Field box will take the value that is input in to the Temperature Change box and add it to the original Temperature field, denoted as "[Tma_ºC_]".  Is that correct?

Also, I connected the New Temp Field variable to the Calculate Field box with an Input Table connector, so I guess that the Calculate Field box is using New Temp Field as the input table, which would not work because it is an empty field.  I did, however, try to run the model with the Calculate Field box connected directly to the Plots variable, but got the same error. 

Thanks, any help is greatly appreciated...