special ruler for 42" Plasma to make ratio correct

I was fooling around with a movie that is non-anmorphic and decided to actually measure the screen size to 'get it right' with the TV's zoom feature expander.
So I started measuring the screen.
Then I used a stick with markings, then I decided to create a "Ratio ruler" for 1.85, and 2.35 aspect ratios.
Turns out my 16x9 screen is a bit taller than a true 1.7777778 at something like 1.73.
So I have the scale (marked ruler)to be able to make non-anamorphic movies 'exactly' the proper aspect ratio.
Works and is better than guessing at the right adjustment by hoping to see a circle in the film... (duh!)
Just a neat tip to pass along.
(I have a Sony 42" Plasma with full, zoom and wide zoom available. The Zoom and Wide Zoom have adjustabe size.)
(Anamorphic movies I leave alone in 'full' to minimize added 'grainyness in zoom and widezoom.