Index: trunk/BNC/src/bnchelp.html
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--- trunk/BNC/src/bnchelp.html	(revision 10946)
+++ trunk/BNC/src/bnchelp.html	(revision 10955)
@@ -5096,4 +5096,19 @@
 Default is an empty option field, meaning that no satellite is excluded from this individual AC.</p>
 <p>
+Use the 'Attitude' field to select how satellite attitude is modelled when converting Antenna Phase Center (APC) corrections to
+Center-of-Mass (CoM) positions required for SP3 output. Three options are available:
+<ul>
+<li><b>Computed</b> (default): BNC applies its own kinematic attitude model:
+GPS noon/midnight turn manoeuvres (Kouba 2009/2015, Bar-Sever 1996),
+GLONASS yaw-fixed mode (Dilssner et al. 2011), and
+Galileo / BDS orbit-normal mode switching (Kouba 2017, Dai et al. 2015, Steigenberger et al. 2018).</li>
+<li><b>Nominal</b>: a simplified, continuous Sun-pointing model is used without any manoeuvre modelling.</li>
+<li><b>SSR</b>: the yaw angle transmitted in the SSR phase bias message is used directly, if present for the satellite and epoch.
+If no yaw angle is available for a particular satellite in a given epoch, BNC falls back to 'Computed'.
+Select this option only if you trust the yaw values provided by the Analysis Center.</li>
+</ul>
+Note that the attitude model affects APC-referenced correction streams only.
+For CoM-referenced streams (SSRC) the Analysis Center has already applied its own attitude model before encoding.</p>
+<p>
 Note that the orbit information in the resulting combination stream is just copied from one of the incoming streams.
 The stream used for providing the orbits may vary over time: if the orbit providing stream has an outage