show the balance

i have a form that is key in the material in record. in this form, that have
a button that is click to open another form which is key the material out
record. one type of material we have different supplier and we record
accordingly by the DO_no and run it by FIFO. means that which material come
in first, then we will use first. now i have a question that can show out the
material balance in the material key in form? for example:

i have 1000kgs, and out 500. that in the material in form there can show out
500? if can show in the material in form, then i no need click into the
material out form to calculate the balance, then come out to material in form
again. i can directly knew that this material i still have less how many for
this DO no.

can make it? thanks for the help!