diff --git a/rugnux/rugnux_cli.cpp b/rugnux/rugnux_cli.cpp
index cc30c1bb5..9fb9bac46 100644
--- a/rugnux/rugnux_cli.cpp
+++ b/rugnux/rugnux_cli.cpp
@@ -2163,15 +2163,22 @@ int RugnuxInputRun::PrepareRugnuxInput() {
     output_provenance.collection_date = dataset->arm_date;
     {
         // The header as the file states it, before anything is measured: what a question about a run
-        // is answered from first.
+        // is answered from first. The wavelength is the one used: --wavelength, where given, is not
+        // refined later, so the file's value would be printed for a run that never used it (--mode scale
+        // keeps the wavelength its reflections were integrated at).
         const auto &x = dataset->experiment;
         const auto gonio = x.GetGoniometer();
         const auto [direct_x, direct_y] = x.GetDiffractionGeometry().GetDirectBeam_pxl();
-        logger.Info("Header: {} images, detector {} {} x {} px of {:.4f} mm, wavelength {:.5f} A, distance "
+        const bool wavelength_given = wavelength_A && mode != RugnuxMode::Scale;
+        const float used_wavelength_A = wavelength_given ? *wavelength_A : x.GetWavelength_A();
+        const std::string wavelength_source =
+                wavelength_given ? fmt::format(" (--wavelength; the file states {:.5f} A)", x.GetWavelength_A()) : "";
+        logger.Info("Header: {} images, detector {} {} x {} px of {:.4f} mm, wavelength {:.5f} A{}, distance "
                     "{:.3f} mm, beam {:.2f} {:.2f} px (direct beam {:.2f} {:.2f}), tilt {:.4f} {:.4f} deg, {}, "
                     "polarization {}",
                     reader.GetNumberOfImages(), x.GetDetectorDescription(), x.GetXPixelsNum(), x.GetYPixelsNum(),
-                    x.GetPixelSize_mm(), x.GetWavelength_A(), x.GetDetectorDistance_mm(), x.GetBeamX_pxl(),
+                    x.GetPixelSize_mm(), used_wavelength_A, wavelength_source, x.GetDetectorDistance_mm(),
+                    x.GetBeamX_pxl(),
                     x.GetBeamY_pxl(), direct_x, direct_y, x.GetPoniRot1_rad() * 180.0 / PI,
                     x.GetPoniRot2_rad() * 180.0 / PI,
                     gonio ? fmt::format("rotation from {:.3f} deg by {:.4f} deg per image", gonio->GetStart_deg(),
@@ -2181,7 +2188,7 @@ int RugnuxInputRun::PrepareRugnuxInput() {
                                               : std::string("not stated"));
         console->OnNote(fmt::format("{} images, {} {} x {} px", reader.GetNumberOfImages(),
                                     x.GetDetectorDescription(), x.GetXPixelsNum(), x.GetYPixelsNum()));
-        console->OnNote(fmt::format("{:.4f} A, {:.1f} mm, {}", x.GetWavelength_A(), x.GetDetectorDistance_mm(),
+        console->OnNote(fmt::format("{:.4f} A, {:.1f} mm, {}", used_wavelength_A, x.GetDetectorDistance_mm(),
                                     gonio ? fmt::format("{:.3f} deg per image", gonio->GetIncrement_deg())
                                           : std::string("no rotation axis")));
     }