diff --git a/src/con_duct/_formatter.py b/src/con_duct/_formatter.py
index c804dc2b..8bf2713e 100644
--- a/src/con_duct/_formatter.py
+++ b/src/con_duct/_formatter.py
@@ -9,11 +9,9 @@
 lgr = logging.getLogger("con-duct")
 
 
-# Decimal (SI) byte units, single source of truth for byte humanization in
-# duct. Used by SummaryFormatter.naturalsize for run-summary output and by
-# the plot axis formatter for tick labels, so a "kB" means the same thing
-# in both places. A future opt-in could add a 1024-base + IEC-suffix
-# variant (KiB/MiB/GiB/...) and let callers pick.
+# Decimal (SI) byte units shared by SummaryFormatter.naturalsize (run
+# summary) and the plot axis formatter, so "kB" means the same thing in
+# both places.
 FILESIZE_UNITS: list[tuple[str, int]] = [
     ("B", 1),
     ("kB", 1000**1),
diff --git a/src/con_duct/_utils.py b/src/con_duct/_utils.py
index 80c57773..90693cf1 100644
--- a/src/con_duct/_utils.py
+++ b/src/con_duct/_utils.py
@@ -79,34 +79,27 @@ def pdcpu_from_pcpu(
     """Delta-corrected %CPU between two ps samples of the same pid.
 
     Inverts the procps identity ``pcpu = cputime / etime * 100`` to
-    recover cputime at each sample, takes the cputime delta, and
-    divides by the elapsed interval. The ``/100`` and ``*100``
-    cancel, so the result is in the same units as ``pcpu``.
+    recover cputime at each sample, deltas it, and divides by the
+    elapsed interval. Result is in the same units as ``pcpu``.
 
     Linux-only: assumes ``pcpu`` is the cumulative ``cputime/etime``
     ratio. Invalid on Darwin (decayed EWMA).
 
-    Identity is the caller's responsibility: invoke ``is_same_pid``
-    first. If the inputs satisfy that precondition, ``Δetime`` is
-    positive and the math is well-defined.
+    Identity is the caller's responsibility -- invoke ``is_same_pid``
+    first.
 
     :param prev_pcpu: %CPU from the earlier sample.
     :param prev_etimes: elapsed seconds at the earlier sample.
     :param curr_pcpu: %CPU from the later sample.
     :param curr_etimes: elapsed seconds at the later sample.
     :returns: delta-corrected %CPU over the interval, or ``None``
-        in two "no measurement" cases:
-
-        - ``Δetime <= 0`` -- defensive guard for callers that
-          skipped ``is_same_pid``; covers sub-quantum and obvious
-          pid-reuse.
-        - Computed ``pdcpu < 0`` -- aggregation-timing artifact.
-          When duct's per-pid ``pcpu`` is max-across-samples while
-          ``etime`` is from the last sample, a spike-then-idle
-          pattern earlier in the run inflates ``prev_pcpu *
-          prev_etimes`` enough that the cputime "delta" goes
-          negative. The pid is the same; the math is just noisy.
-          A small minus dip is honestly null, not zero.
+        when no measurement is recoverable:
+
+        - ``Δetime <= 0`` -- defensive guard; covers sub-quantum and
+          obvious pid-reuse for callers that skipped ``is_same_pid``.
+        - Computed ``pdcpu < 0`` -- aggregation-timing artifact from
+          duct's max-pcpu / end-etime mismatch on spike-then-idle
+          patterns. Honestly null, not zero.
     """
     interval = curr_etimes - prev_etimes
     if interval <= 0:
diff --git a/src/con_duct/plot.py b/src/con_duct/plot.py
index b3ebf756..b13fa58d 100644
--- a/src/con_duct/plot.py
+++ b/src/con_duct/plot.py
@@ -174,10 +174,6 @@ def _envelopes(
     omitted entirely rather than reported as zero -- a missing measurement
     is not the same as zero load.
 
-    The grid is the union of (kept pids') elapsed values; the alternative
-    of "every entry timestamp regardless of who appeared" would only add
-    grid points that are missing measurements anyway.
-
     :returns: ``(grid_xs, max_ys, sum_ys)`` aligned, sorted by ``grid_xs``.
     """
     grid: Dict[float, List[float]] = {}
@@ -337,22 +333,12 @@ def matplotlib_plot(args: argparse.Namespace) -> int:
             alpha=0.4,
         )
 
-    # Envelopes: max-across-pids (lower bound) solid, upper bound dashed.
-    # If some pid was at 50%, the total was at least 50% -- max-of-pids is
-    # a true lower bound on the concurrent total in both metrics.
-    #
-    # Upper bounds: for both rss and (in ps-pcpu mode) cpu, we use duct's
-    # per-record ``totals[field]`` -- the peak concurrent value observed
-    # at any single sub-sample within the report interval. This is a
-    # tight upper bound under "observed samples only" framing, and avoids
-    # the phantom-coexistence inflation of summing per-pid peaks (pids
-    # whose peaks fell in different sub-samples within the interval would
-    # otherwise both contribute their peak).
-    #
-    # In ps-cpu-timepoint mode there is no per-record ``totals.pdcpu`` --
-    # pdcpu is computed at plot time -- so we fall back to summing per-pid
-    # pdcpu. The negative-pdcpu clamp filters the worst aggregation-timing
-    # artifacts; remaining looseness is a known, accepted caveat.
+    # Solid = max-across-pids (lower bound on the concurrent total).
+    # Dashed = upper bound: per-record ``totals[field]`` for rss and
+    # ps-pcpu cpu; in ps-cpu-timepoint mode there is no
+    # ``totals.pdcpu`` (computed at plot time), so fall back to
+    # sum-across-pids. See docs/resource-statistics.md for the
+    # phantom-coexistence rationale.
     pcpu_xs, pcpu_max, pcpu_sum = _envelopes(pid_series, "cpu")
     if pcpu_xs:
         ax.plot(  # type: ignore[call-arg]
@@ -389,10 +375,7 @@ def matplotlib_plot(args: argparse.Namespace) -> int:
     ax.set_ylabel(f"{args.cpu} (%)")
     ax2.set_ylabel("rss")
     if pid_series:
-        # Two legends, color-agnostic linestyle key on the right and metric
-        # color key on the left. Linestyle entries are listed in the order
-        # a viewer's eye scans the chart: upper bound (the high dashed line),
-        # lower bound (the solid line below it), per-pid (dotted cloud).
+        # Two legends: linestyle key on the right, metric color key on the left.
         style_handles = [
             Line2D(
                 [0],