Thank you for the fast replies,
I have been looking at both solutions offered but I´m not sure if the calculate value tool is the right one for what I´m trying.
The script is as follows:
# Import system modules
# Get input arguments - table name, field name
Equation = arcpy.GetParameterAsText(0)
Input = arcpy.GetParameterAsText(1)
#check if equation is chosen:
if Input == Equation:
But I get an error saying there is a problem with the if statement.
Both inputs are defined as strings but "input" is chosen from a drop down list when the model starts.