How does posting the source to vote counting software help anything? The real issue isn't that people want some source that's capable of counting votes accurat

How does posting the source to vote counting software help anything? The real issue isn't that people want some source that's capable of counting votes accurately. The problem is that the machines aren't necessarily counting all the votes; having some open source software laying around somewhere doesn't guarantee that the machines themselves are running audited and trusted code. How can anything other than a physical, tamper-resistant audit trail help make vote tallies trustworthy?