I use an electric focuser because it adjust focus without introducing vibrations.
To fully determine the exact point where the image is focused I use a Hartmann mask with four triangles, because the diffraction peaks generated greatly facilitate the determination of exact focus.
You can make a template for this kind of mask here.
The next image shows a focusing sequence clearly showing how the twin peaks merge when they reach the focus.
Click on the image to see it larger.
I have also tested a Bahtinov mask which was excellent for an even easier focusing. Now I use allways this mask.
