A hash code is a mathematical integer which acts like an identity for an object. It differs from one object to another.
A hash code is displayed in the comfort letter that comes with every archive we create.
You can use this code to check whether the file present on the USB, is in fact the file we created.
Comparing hash codes is a convenient way of checking if the file has changed. As every change, however small it may be, results in a completely different hash code.