Canon EOS 90D Advanced User's Manual page 537

Only horizontal tilt can be checked. (Forward/backward tilt is not displayed.)
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There may be a margin of error of approx. ±1°.
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An asterisk next to [ 5 : Viewfi nder display] indicates that the default
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viewfi nder display setting has been changed.
Grid Display
You can display a grid in the viewfi nder to help you check the camera tilt or
compose the shot.
You can display a grid on the screen during Live View shooting and before you
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start recording a movie ( = 540).
Displaying the Flicker Detection M
If you set this function, < G > will appear in the viewfi nder when the
camera detects fl icker caused by the blinking of the light source.
If you set [ z : Anti-fl icker shoot.] to [Enable], you can shoot with reduced
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unevenness of exposure caused by the fl icker ( = 261).
Customization of Information in the Viewfi nder
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