When you move off of a record, it is saved, barring any issues. Moving off can be done in a few ways: navigate to another record on a continuous or single form, or even move off of a subform onto the main form, all which happens behind the scenes. Sometimes the only ways to avoid this are unbound forms or forms based on staging tables, where nothing is saved into the main tables until all is well.
Your biggest issue is that you should not be storing stock quantity calculations. The count should be derived from the INS minus the OUTS. See what you think of this before continuing on your current path
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The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.