How to work UPDATE function in UDF
 

I need to define the some property UDF such as density, thermal conductivity, diameter, heat capacity, but problem is these properties is function of other parameter moisture content that will fist calculate then these values comes. What function should I define in UDF so that moisture will change every cell. Is it UPDATE function or something else?
I make the code, it compiled but floating point errors coming. I thought update function is not working. Could you please suggest me how can I solve this problem.