Sjizzle already did calculating a fix using the new sextant included in the TDW 7_5_0 version wich is only released as a test version at the moment.
The this post where he shows a screen of his nav map drawing for a night fix.
http://www.subsim.com/radioroom/show...ostcount=10609
In another thread he stated that he might make a sextant tutorial soon
http://www.subsim.com/radioroom/showthread.php?t=206103
Another thread you might be interested in is a WIP in progress by myself. Bringing more information onto the navmap. As a begin I started with adding all the nav buoys at their postition on the map
http://www.subsim.com/radioroom/showthread.php?t=206373