What’s the correct direction to file nails?

Years ago the American beauty magazines said the correct way to file nails was only in one direction to keep the nail from splitting. Now there are tons of Vietnamese shops and they file toward the center of the finger. I even asked one politely and she said that is how they have been taught.  However, I think this is superstition to keep the nail pointy to ward off evil spirits. I even see manicurists file back and forth like a saw, which I think is bad for the natural nail.