How do I check if the door gasket (seal) is working properly?

Hold a strip of paper approximately 50mm wide against the door frame and close the door on it — an effective gasket should grip the paper and you should feel some resistance when you gently pull it. Repeat this test at 200mm intervals all around the door, as the most unfavourable points can also be found by inspecting the seal area with the door closed and the interior illuminated. If the door does not seal properly, the gasket may need replacing or the door may need adjustment, and this check should be performed at least once a week. (Page 37)