BUG: Fix bug with interval calculation (#13062)

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

azure-pipelines.yml

@@ -243,7 +243,7 @@ stages:
           PYTHONIOENCODING: 'utf-8'
           AZURE_CI_WINDOWS: 'true'
           PYTHON_ARCH: 'x64'
-        timeoutInMinutes: 75
+        timeoutInMinutes: 80
         strategy:
           maxParallel: 4
           matrix:

doc/changes/devel/13062.bugfix.rst

@@ -0,0 +1 @@
+Fix computation of time intervals in :func:`mne.preprocessing.compute_fine_calibration` by `Eric Larson`_.

mne/preprocessing/_fine_cal.py

@@ -156,11 +156,12 @@ def compute_fine_calibration(
     # 1. Rotate surface normals using magnetometer information (if present)
     #
     cals = np.ones(len(info["ch_names"]))
-    time_idxs = raw.time_as_index(np.arange(0.0, raw.times[-1], t_window))
-    if len(time_idxs) <= 1:
-        time_idxs = np.array([0, len(raw.times)], int)
-    else:
-        time_idxs[-1] = len(raw.times)
+    end = len(raw.times) + 1
+    time_idxs = np.arange(0, end, int(round(t_window * raw.info["sfreq"])))
+    if len(time_idxs) == 1:
+        time_idxs = np.concatenate([time_idxs, [end]])
+    if time_idxs[-1] != end:
+        time_idxs[-1] = end
     count = 0
     locs = np.array([ch["loc"] for ch in info["chs"]])
     zs = locs[mag_picks, -3:].copy()
@@ -388,9 +389,11 @@ def _adjust_mag_normals(info, data, origin, ext_order, *, angle_limit, err_limit
     each_err = _data_err(data, S_tot, cals, axis=-1)[picks_mag]
     n_bad = (each_err > err_limit).sum()
     if n_bad:
+        bad_max = np.argmax(each_err)
         reason.append(
             f"{n_bad} residual{_pl(n_bad)} > {err_limit:0.1f}% "
-            f"(max: {each_err.max():0.2f}%)"
+            f"(max: {each_err[bad_max]:0.2f}% @ "
+            f"{info['ch_names'][picks_mag[bad_max]]})"
         )
     reason = ", ".join(reason)
     if reason:

mne/preprocessing/tests/test_fine_cal.py

@@ -20,7 +20,7 @@
 )
 from mne.preprocessing.tests.test_maxwell import _assert_shielding
 from mne.transforms import _angle_dist_between_rigid
-from mne.utils import object_diff
+from mne.utils import catch_logging, object_diff
 
 # Define fine calibration filepaths
 data_path = testing.data_path(download=False)
@@ -289,3 +289,15 @@ def test_fine_cal_systems(system, tmp_path):
     got_corrs = np.corrcoef([raw_data, raw_sss_data, raw_sss_cal_data])
     got_corrs = got_corrs[np.triu_indices(3, 1)]
     assert_allclose(got_corrs, corrs, atol=corr_tol)
+    if system == "fil":
+        with catch_logging(verbose=True) as log:
+            compute_fine_calibration(
+                raw.copy().crop(0, 0.12).pick(raw.ch_names[:12]),
+                t_window=0.06,  # 2 segments
+                angle_limit=angle_limit,
+                err_limit=err_limit,
+                ext_order=2,
+                verbose=True,
+            )
+        log = log.getvalue()
+        assert "(averaging over 2 time intervals)" in log, log