D7 checkbox default checked Shouldn't be hard, but it is - how do you make a CCK checkbox default checked?!?

I've tried various responses in the PHP Default Value box:

return array(0 =&gt; array('#default_value' =&gt; 1));
return array(0 =&gt; array('default_value' =&gt; 1));
return array(0 =&gt; array(1));
return array(0 =&gt; 1));
return array(1);
return 1;


I'm sure you get the point. None of these work?!
I'm a bit confused where you're entering the code above? If I want a checkbox to default to checked then in the UI you can specify this. See screen shot where I've added a field with a label "Shippable".