diff --git a/repyability/rbd/_point_availability.py b/repyability/rbd/_point_availability.py
index dd94b58..5ce57a7 100644
--- a/repyability/rbd/_point_availability.py
+++ b/repyability/rbd/_point_availability.py
@@ -835,7 +835,9 @@ def __init__(
         # numbers about ``top ** 2``, so it is uncertain by a few units of
         # rounding in them (numpy 2.0 sums them to 1e-15 at a top of 5).
         if variance <= (1e-6 * self.top) ** 2:
-            self.fixed = mean
+            # A time known exactly is its atom's, not the mean's rounding.
+            atoms = _atoms(lambda s: 1.0 - sf(s), self.splits, self.top)
+            self.fixed = atoms[0][0] if len(atoms) == 1 else mean
             return
         from scipy.signal import fftconvolve
 
diff --git a/repyability/tests/test_preventive_maintenance.py b/repyability/tests/test_preventive_maintenance.py
index e4c2e2f..7b4a229 100644
--- a/repyability/tests/test_preventive_maintenance.py
+++ b/repyability/tests/test_preventive_maintenance.py
@@ -138,16 +138,19 @@ def test_maintenance_that_takes_time_is_a_planned_outage():
     assert per_run(result, result.system_restorations) == 9
     assert result.system_failures == 0
     assert result.mean_up_time == 40.0
-    assert result.cost.by_category == {
-        "repair": 0.0,
-        "replace": 0.0,
-        "preventive": 50.0,
-        "inspection": 0.0,
-        "component_downtime": 60.0,
-        "system_downtime": 140.0,
-        "setup": 0.0,
-    }
-    assert result.cost.by_component == {"c": 110.0}
+    # The costs are the exact means, integrated: to rounding.
+    assert result.cost.by_category == pytest.approx(
+        {
+            "repair": 0.0,
+            "replace": 0.0,
+            "preventive": 50.0,
+            "inspection": 0.0,
+            "component_downtime": 60.0,
+            "system_downtime": 140.0,
+            "setup": 0.0,
+        }
+    )
+    assert result.cost.by_component == pytest.approx({"c": 110.0})
     fci = result.criticalities.failure_criticality_index
     # Planned outages are not failures.
     assert fci.per_system_failure.get("c", 0) == 0