The photos look fine. For the grid, just draw some perpendicular lines using a Sharpie and a yardstick.
Then take photos of the grid at max wide angle and max zoom. You want the grid to fill the photo in both cases.
Take pictures of the grid at full zoom in both hand held and tripod to see how effective your stabilization is.
It's harder to tell what the camera is capable of when you take "normal" pictures.
Looks like you're doing fine regardless.