fix

tests/test_processing.py

@@ -20,6 +20,8 @@ from rfg_adc_plotter.gui.pyqtgraph_backend import (
     convert_tty_i16_to_voltage,
     decimate_bscan_rows_for_display,
     decimate_curve_for_display,
+    display_distance_axis,
+    display_distance_value,
     fft_bscan_image_to_db,
     is_short_sweep,
     resolve_axis_bounds,
@@ -546,6 +548,13 @@ class ProcessingTests(unittest.TestCase):
         self.assertTrue(bool(keep_mask[-1]))
         self.assertAlmostEqual(float(cut_axis[0]), 3.0, places=6)
 
+    def test_display_distance_axis_zero_is_at_nine_meters(self):
+        axis = np.asarray([0.0, 4.5, 9.0], dtype=np.float64)
+        display_axis = display_distance_axis(axis)
+
+        np.testing.assert_allclose(display_axis, np.asarray([9.0, 4.5, 0.0], dtype=np.float64))
+        self.assertAlmostEqual(display_distance_value(9.0), 0.0, places=12)
+
     def test_resolve_initial_window_size_stays_within_small_screen(self):
         width, height = resolve_initial_window_size(800, 480)