I 
think the 'rotation snaps every' setting cannot accept arbitrary values. They 
have to be integer divisions of 360 degrees:
360 / 2 = 180 deg
360 / 3 = 120 deg
360 / 4 = 90 deg
360 / 5 = 72 deg
360 / 6 = 60 deg
etc.
25 degrees is not possible, because if you go in steps 
of 25 around a circle, after one round you won't end up where you 
started:
0
25
50
...
350
375 = 15
40
65
...
Inkscape would snap to lots of angles this 
way.
 
Have you seen Inkscape's axonometric grid? Maybe 
that can help you out a bit.
 
Regards,
Johan Engelen
 
  
  
I do have some questions concerning technical 
  linedrawings with inkscape: 
1. I 
  take a screenshot of 3D-CAD a model that is rotated in a standard axonometric 
  view. For example an isometric projection 30°-30°. 
2. I import the screenshot into inkscape. 
  
3. In "inkscape preferences" dialog in option 
  "steps" Is set "rotation snaps every" to 30°. 
4. By holding down "Strg" I can easily trace the screenshot. 
  
However when I have the 3D-CAD model 
  rotated to some other axonometric view, for example 25-25°. This 
  
helpful technique is no more possible, since 
  I can only choose from a list of predifined values in "rotation snaps 
  every". 
I´d like to put in any kind of 
  value. 
Should this be on the 
  wishlist? 
Another question: 
  
I want to move an object along a defined 
  axis. 
When I hold down "strg" I can 
  move a selected object along the vertical and horizontal axis. 
  
Are there ways and techniques in inkscape to 
  do that kind of thing along any kind of axis. 
Thanks for your help 
Marcel 
Lindauer 
  DORNIER GmbH 
Rickenbacher 
  Str. 119 
88129 
  Lindau / Germany
Phone: 
  +49 8382 703-0
Fax: 
      +49 8382 703-4 15 
webmaster@...2272... 
  
http://www.lindauerdornier.com 
  
Commercial 
  Registry:
HR 
  Kempten Nr. B/1220 
Chairman 
  of the Supervisory Board: Prof. Dr. Dieter Feddersen,
Managing 
  Directors: Peter 
  D. Dornier (CEO), Michael Ebeling, Dr. Andreas Rutz, Hans-Jürgen Schmidt 
  (CFO)