When you walk up to a tool, you should be able to rely on it doing what you ask it to do. With your bandsaw, you should be confident that the blade is square to the table. Instead of using a square and checking the relationship between the blade and the table you can do this check with nothing more than a piece of scrap.
The benefit of using this approach
When you use this technique you’re doing the test with the saw running, not sitting idle. That means you’re simulating the scenario you’ll be in when you’re making cuts with the bandsaw. That’s the best way to check your setup. When setting up a bandsaw, or any tool, it’s best to get the test environment as close as you can to the real environment.
What you need
This simple test requires nothing but a scrap board. The wider the board, the more accuracy you’ll get from the test. One edge of the board should be straight. It’s best if it’s been jointed. It doesn’t matter what blade you have in the saw for the test.
Use this approach on other tools
Once you understand this approach for setting up a bandsaw, you can apply this concept to other tools. For instance, you can use a very similar technique to make sure your miter saw is cutting square.