We have a NAV dry goods-intake screen where I work which is not automatically picking up the weight of a scale attached to the serial port of the computer. It is set up properly in the NAV terminal configuration card but when we go to book in stock the weight is not automatically pulling through onto the screen.
With bespoke work like this the only real solution is to contact the person that developed the code.
I think some time due to compatibility of scale or any error in software you don't get the results properly on your computer. So you must read user manual as it help you in resolving this problem.
You can also find some information about compatibility of your scale at your scale manufacturer website. Or some time they offer online support for technical issues.