availability after orders field in machine center

Dear all, I would like to add availability after orders (AAO) field in the machine center card form. The original of AAO is from machine center load, but there is a code to generate it in the machine center card load. I find that capacity (Total) and production order qty need can be appeared in the field because they are available in the machine center table. I have added the AAO field in the machine center table and inserted it in the machine center card form. I write a formula as follows: AAO onvalidate() “AAO” := ROUND(“Capacity (Total)” - “Production Order qty need (Total)”); Capacity (Total) onvalidate() “AAO” := ROUND(“Capacity (Total)” - “Production Order qty need (Total)”); Production order qty need (Total) onvalidate() “AAO” := ROUND(“Capacity (Total)” - “Production Order qty need (Total)”); But I can’t find the result when running the formula in the machine center. Is it because the capacity and production order… 's property “flowfield” ? Pls let me know how to solve and if there is another formula or code I await so much. tks beforehand Rgds, Mark