Fix max range, range cursor, and stc range control readouts

include/data_structure_and_constants.h

@@ -194,9 +194,14 @@ extern float uniform_noise_filter;
 // Components: Chain Home A-scope
 extern float uniform_radiogoniometer;
 
-// Maximum radar range, all scopes except Chain Home — keyboard o (lower) / p (higher)
-// GLSL uniform: float max_range
-// Components: Marine A-scope, PPI scopes
+/*
+ * Maximum radar range in nautical miles (NOT normalized).
+ * Chain Home is fixed at CHAIN_HOME_MAX_RANGE_NM; the o/p keys have no effect for it.
+ * For other radars the value is taken from the radar's step table and updated by o/p.
+ * Set via reset_radar_controls() when a radar is activated.
+ * GLSL uniform: float max_range
+ * Components: all scope renderers
+ */
 extern float uniform_max_range;
 
 // Range cursor, PPI scopes only — keyboard a (lower) / s (higher)