errare mathematicum est

So today after lecture i wanted to test some mechanics for linear algebra and just wrote down some random numbers and tested calculating some results with different mechanics and i always got nonsense results. I actually did not make a mistake in how to use these, but i always got mixed up with some numbers, eventhough i used a calculator and in my exam i am not even allowed to use a calculator, so i will probably get similar mistakes in my exam. x( And it really will not be great to not manage to get to the 50% that is needed just because i calculate stuff wrong. haha