How to keet my choose in Combo Box in MathCad 15

Hi everybody

I usually use Combo boxes in mathcad 15, bu t the problem is that if you choose something in there even after you save your file , the combo box selection will back to the default when you open it again ( because of script behind it)

for example in below image what should I write in script to keep my choose before last save?

any help in this regards will be highly appreciated

Thanks