I'm getting acquainted with my 4x5 camera. I want to use a compoosition card so that I don't need to tear down the camera everytime i want to visualise how the picture will turn out. I read a composition card can be an useful tool.

My first attempt:
I looked through my camera, and make a mock up of a card at arms length.
few problems. It isn't anywhere near accurate enough. The aspect ratio of 4x5 isn't maintained either.

I need:
instructions, and guide to how to use it.