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2Rulers
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4
5You can overlay horizontal and vertical rulers on a web page:
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7.. image:: viewport_rulers.png
8  :class: center
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10The units are in pixels.
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12The dimensions of the viewport are displayed near the top-right corner of the viewport.
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14To be able to toggle rulers for a page, you first need to enable the button by going to the settings page for the Developer Tools and checking "Toggle rulers for the page" under Available Toolbox Buttons.
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16.. image:: settings_available_buttons.png
17  :class: center
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19Once enabled, the "Toggle rulers for the page" button appears at the top right of the Toolbox, in the same place as the Settings/Options button.
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21.. image:: ruler_toggle_button.png
22  :class: center
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24
25Behavior to keep in mind when using rulers:
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27- The rulers command must be reapplied in **new tabs** and after **each page refresh.**
28- The command isn't permanent.
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