Sill or Header Heights

In the Preview and Positioning panel, the pop-up lets you choose any one of these as a point of reference for the sill/header value.
Sill to (current) Story: the height of the Sill will be measured relative to the level of the Current Story (the last story open on the Floor Plan). To choose a different Story, click the Select Story option and choose a story from the dialog box.
Header to Story: same method as the Sill to Current Story options, but you must provide the Header height. To choose a different Story, click the Relink Anchor Story option and choose a story from the dialog box
Relink Anchor Story: If you choose this option (select the Story name from the list in the appearing dialog box), the chosen story’s height will serve as the Anchor from which the Window/Door should be measured. This option may be used, for example, when a Glass Curtain Wall is created and all individual panes must have their heights set to a common height.