Checkbutton manpage says: Name: offValue Class: Value Switch: -offvalue Specifies value to store in the button's associated variable whenever this button is deselected. Defaults to ``0''. Name: onValue Class: Value Switch: -onvalue Specifies value to store in the button's associated variable whenever this button is selected. Defaults to ``1''.

As said by Anonymous monk, just link it to same variable and you are done: 

$t->Checkbutton(-text => 'Top',-variable => \$m)->pack(-side => 'left'
+)})->pack();

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In reply to Re: How to keep two checkbuttons in sync by gurpreetsingh13
in thread How to keep two checkbuttons in sync by ghosh123

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