Add a function declaration

diff --git a/src/Instrumentation/attitude_indicator.cxx b/src/Instrumentation/attitude_indicator.cxx
index 36a8a2d8686a28965a72e2d9c65c8d09c0a8c8de..3badf205557b7bcd16d9d81bcd2278eeeabfdd40 100644 (file)
--- a/src/Instrumentation/attitude_indicator.cxx
+++ b/src/Instrumentation/attitude_indicator.cxx
@@ -6,6 +6,8 @@
 // TODO:
 // - better spin-up
 
+#include <math.h>      // fabs()
+
 #include "attitude_indicator.hxx"
 #include <Main/fg_props.hxx>
 #include <Main/util.hxx>