diff --git a/chainladder/utils/data/_manifest.py b/chainladder/utils/data/_manifest.py
index 7cc2b9064..5a1b27176 100644
--- a/chainladder/utils/data/_manifest.py
+++ b/chainladder/utils/data/_manifest.py
@@ -1,4 +1,5 @@
-"""Central registry of bundled sample datasets.
+"""
+Central registry of bundled sample datasets.
 
 Single source of truth for the metadata of every CSV in
 ``chainladder/utils/data/``. Consumed by:
@@ -139,6 +140,13 @@
         ],
         "cumulative": True,
     },
+    "friedland_dc_insurer": {
+        "origin": "Accident Year",
+        "development": "Valuation",
+        "index": None,
+        "columns": ["Reported Claims"],
+        "cumulative": True,
+    },
     "friedland_gl_insurer": {
         "origin": "Accident Year",
         "development": "Calendar Year",
diff --git a/chainladder/utils/data/friedland_dc_insurer.csv b/chainladder/utils/data/friedland_dc_insurer.csv
new file mode 100644
index 000000000..41c627588
--- /dev/null
+++ b/chainladder/utils/data/friedland_dc_insurer.csv
@@ -0,0 +1,140 @@
+Accident Year,Valuation,Reported Claims
+1997,1997-03,861
+1997,1997-06,1668
+1997,1997-09,2459
+1997,1997-12,3255
+1997,1998-03,3366
+1997,1998-06,3385
+1997,1998-09,3385
+1997,1998-12,3374
+1997,1999-03,3372
+1997,1999-06,3374
+1997,1999-09,3376
+1997,1999-12,3376
+1997,2007-12,3376
+1997,2008-12,3376
+1998,1998-03,878
+1998,1998-06,1493
+1998,1998-09,2248
+1998,1998-12,2756
+1998,1999-03,2826
+1998,1999-06,2812
+1998,1999-09,2805
+1998,1999-12,2804
+1998,2000-03,2785
+1998,2000-06,2787
+1998,2000-09,2787
+1998,2000-12,2788
+1998,2007-12,2788
+1998,2008-12,2788
+1999,1999-03,463
+1999,1999-06,786
+1999,1999-09,1166
+1999,1999-12,1605
+1999,2000-03,1673
+1999,2000-06,1642
+1999,2000-09,1646
+1999,2000-12,1645
+1999,2001-03,1649
+1999,2001-06,1649
+1999,2001-09,1649
+1999,2001-12,1649
+1999,2007-12,1649
+1999,2008-12,1649
+2000,2000-03,511
+2000,2000-06,806
+2000,2000-09,1112
+2000,2000-12,1530
+2000,2001-03,1684
+2000,2001-06,1689
+2000,2001-09,1686
+2000,2001-12,1688
+2000,2002-03,1686
+2000,2002-06,1687
+2000,2002-09,1687
+2000,2002-12,1687
+2000,2007-12,1687
+2000,2008-12,1687
+2001,2001-03,414
+2001,2001-06,750
+2001,2001-09,1264
+2001,2001-12,1836
+2001,2002-03,2088
+2001,2002-06,2078
+2001,2002-09,2081
+2001,2002-12,2086
+2001,2003-03,2086
+2001,2003-06,2087
+2001,2003-09,2087
+2001,2003-12,2088
+2001,2007-12,2088
+2001,2008-12,2096
+2002,2002-03,502
+2002,2002-06,961
+2002,2002-09,1424
+2002,2002-12,2016
+2002,2003-03,2307
+2002,2003-06,2330
+2002,2003-09,2342
+2002,2003-12,2348
+2002,2004-03,2352
+2002,2004-06,2354
+2002,2004-09,2355
+2002,2004-12,2355
+2002,2007-12,2355
+2002,2008-12,2340
+2003,2003-03,614
+2003,2003-06,1231
+2003,2003-09,1940
+2003,2003-12,2576
+2003,2004-03,2878
+2003,2004-06,2936
+2003,2004-09,2977
+2003,2004-12,2988
+2003,2005-03,2992
+2003,2005-06,2992
+2003,2005-09,2994
+2003,2005-12,2994
+2003,2007-12,2994
+2003,2008-12,3007
+2004,2004-03,833
+2004,2004-06,1576
+2004,2004-09,2181
+2004,2004-12,3048
+2004,2005-03,3407
+2004,2005-06,3406
+2004,2005-09,3397
+2004,2005-12,3403
+2004,2006-03,3407
+2004,2006-06,3410
+2004,2006-09,3412
+2004,2006-12,3412
+2004,2007-12,3412
+2004,2008-12,3392
+2005,2005-03,675
+2005,2005-06,1248
+2005,2005-09,1833
+2005,2005-12,2601
+2005,2006-03,2792
+2005,2006-06,2791
+2005,2006-09,2803
+2005,2006-12,2810
+2005,2007-03,2813
+2005,2007-06,2814
+2005,2007-09,2814
+2005,2007-12,2814
+2005,2008-12,2885
+2006,2006-03,764
+2006,2006-06,1374
+2006,2006-09,2157
+2006,2006-12,2531
+2006,2007-03,2897
+2006,2007-06,2930
+2006,2007-09,2945
+2006,2007-12,2949
+2006,2008-12,3030
+2007,2007-03,754
+2007,2007-06,1468
+2007,2007-09,1987
+2007,2007-12,2463
+2007,2008-12,2733
diff --git a/docs/_toc.yml b/docs/_toc.yml
index eec4660c2..72ae4f43a 100644
--- a/docs/_toc.yml
+++ b/docs/_toc.yml
@@ -42,6 +42,7 @@ parts:
       - file: friedland/chapter_9.ipynb
       - file: friedland/chapter_10.ipynb
       - file: friedland/chapter_11.ipynb
+      - file: friedland/chapter_15_monitoring.ipynb
   - chapters:
     - file: gallery/index.md
   - chapters:
diff --git a/docs/friedland/chapter_15_monitoring.ipynb b/docs/friedland/chapter_15_monitoring.ipynb
new file mode 100644
index 000000000..4e32cacfd
--- /dev/null
+++ b/docs/friedland/chapter_15_monitoring.ipynb
@@ -0,0 +1,359 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "id": "ch15m-intro",
+   "metadata": {},
+   "source": [
+    "# Chapter 15 - Monitoring Unpaid Claim Estimates\n",
+    "\n",
+    "> Deviations of actual development from projected development of claims or\n",
+    "> claim counts are one of the most useful diagnostic tools for evaluating the\n",
+    "> accuracy of the unpaid claim estimate.\n",
+    ">\n",
+    "> -- Friedland, Chapter 15\n",
+    "\n",
+    "The last part of Chapter 15 is a **roll-forward**: take the ultimates and\n",
+    "reporting pattern selected at one valuation, and compare actual reported\n",
+    "claims in the next period with the amount that pattern said should emerge.\n",
+    "\n",
+    "This notebook recreates Friedland's **DC Insurer** monitoring exhibits\n",
+    "(*Exhibit IV, Sheets 1-4*). `friedland_dc_insurer` is the quarterly reported\n",
+    "triangle through 36 months, plus the 12/31/2007 and 12/31/2008 diagonals.\n",
+    "Selected CDFs stop at 36 months (age-to-ult 1.000), so later ages are treated\n",
+    "as fully reported.\n",
+    "\n",
+    "Expected emergence in the next calendar period comes from the fitted\n",
+    "`Chainladder` model: `full_triangle_.dev_to_val()` at the later valuation\n",
+    "minus the prior `latest_diagonal`. That is the same pattern as the gallery\n",
+    "Actual vs Expected example. For each accident year that is the Friedland\n",
+    "formula\n",
+    "\n",
+    "$$\n",
+    "\\frac{\\text{Ultimate}_{t_0} - \\text{Reported}_{t_0}}{1 - p_{t_0}}\n",
+    "\\times (p_{t_1} - p_{t_0})\n",
+    "$$\n",
+    "\n",
+    "where $p_t = 1 / \\text{CDF}_t$."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "ch15m-imports",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import numpy as np\n",
+    "import pandas as pd\n",
+    "import chainladder as cl\n",
+    "from IPython.display import display\n",
+    "\n",
+    "pd.set_option(\"display.max_columns\", None)\n",
+    "pd.set_option(\"display.width\", 1000)\n",
+    "\n",
+    "\n",
+    "def as_series(tri):\n",
+    "    s = tri.to_frame(origin_as_datetime=False).iloc[:, 0]\n",
+    "    s.index = [int(getattr(i, \"year\", i)) for i in s.index]\n",
+    "    return s"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "ch15m-sheet1-md",
+   "metadata": {},
+   "source": [
+    "## Exhibit IV, Sheet 1 - Reported claims triangle\n",
+    "\n",
+    "DC Insurer reports quarterly. The sample carries ages 3 through 36, which is\n",
+    "the printed Sheet 1 triangle. The selected tail is 1.000 at 36 months, so\n",
+    "older accident years are carried at that age-36 value through 12/31/2007."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "ch15m-sheet1",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "tri = cl.load_sample(\"friedland_dc_insurer\")\n",
+    "tri = tri[tri.origin < \"2008\"]\n",
+    "tri_2007 = tri[tri.valuation < \"2008\"]\n",
+    "\n",
+    "selected_cdf = {\n",
+    "    3: 4.125,\n",
+    "    6: 2.177,\n",
+    "    9: 1.487,\n",
+    "    12: 1.136,\n",
+    "    15: 1.016,\n",
+    "    18: 1.008,\n",
+    "    21: 1.003,\n",
+    "    24: 1.001,\n",
+    "    27: 1.000,\n",
+    "    30: 1.000,\n",
+    "    33: 1.000,\n",
+    "    36: 1.000,\n",
+    "}\n",
+    "for age in (int(a) for a in tri_2007.ddims):\n",
+    "    selected_cdf.setdefault(age, 1.000)\n",
+    "\n",
+    "dev = cl.DevelopmentConstant(patterns=selected_cdf, style=\"cdf\").fit_transform(tri_2007)\n",
+    "model = cl.Chainladder().fit(dev)\n",
+    "\n",
+    "display(tri_2007[tri_2007.development <= 36])\n",
+    "display(dev.cdf_[dev.cdf_.ddims <= 36])"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "ch15m-sheet2-md",
+   "metadata": {},
+   "source": [
+    "## Exhibit IV, Sheet 2 - Ultimates at 12/31/2007\n",
+    "\n",
+    "DC Insurer selects ultimates with the reported development technique. Age 12\n",
+    "uses a 1.136 CDF (88.0% reported); age 24 uses 1.001 (99.9% reported); age 36\n",
+    "and later are 1.000.\n",
+    "\n",
+    "`model_diagnostics` pulls Latest, CDF, and Ultimate from the fitted\n",
+    "`Chainladder` model. The text's worked example for accident year 2007 is\n",
+    "$2{,}463 \\times 1.136 = 2{,}798$."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "ch15m-sheet2",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "diag = cl.model_diagnostics(model)\n",
+    "years = [int(year) for year in tri_2007.origin.year]\n",
+    "sheet2 = pd.DataFrame(index=years)\n",
+    "sheet2[\"Age\"] = (2007 - sheet2.index + 1) * 12\n",
+    "sheet2[\"Reported at 12/31/07\"] = as_series(diag[\"Latest\"])\n",
+    "sheet2[\"CDF to Ultimate\"] = np.round(as_series(diag[\"CDF\"]), 3)\n",
+    "sheet2[\"Projected Ultimate\"] = np.round(as_series(diag[\"Ultimate\"]), 0)\n",
+    "display(sheet2)\n",
+    "print(f\"Total projected ultimate: {sheet2['Projected Ultimate'].sum():,.0f}\")"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "ch15m-sheet3-md",
+   "metadata": {},
+   "source": [
+    "## Exhibit IV, Sheet 3 - Annual monitoring test\n",
+    "\n",
+    "One year later, compare calendar-year 2008 actual reported claims with the\n",
+    "amount implied by the 12/31/2007 model. Slice `full_triangle_` at the 2008\n",
+    "valuation for the expected cumulative; subtract the 2007 `latest_diagonal`\n",
+    "for expected emergence.\n",
+    "\n",
+    "The text works accident year 2007 as\n",
+    "\n",
+    "$$\n",
+    "\\frac{2{,}798 - 2{,}463}{1 - 0.880} \\times (0.999 - 0.880) = 332\n",
+    "$$\n",
+    "\n",
+    "and accident year 2006 as\n",
+    "\n",
+    "$$\n",
+    "\\frac{2{,}952 - 2{,}949}{1 - 0.999} \\times (1.000 - 0.999) = 3.\n",
+    "$$\n",
+    "\n",
+    "Older years are fully reported, so expected emergence is zero."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "ch15m-sheet3",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "expected_cum = model.full_triangle_.dev_to_val()\n",
+    "expected_cum = expected_cum[expected_cum.valuation == tri.valuation_date]\n",
+    "\n",
+    "reported_2007 = as_series(tri_2007.latest_diagonal)\n",
+    "reported_2008 = as_series(tri.latest_diagonal)\n",
+    "expected = np.round(as_series(expected_cum) - reported_2007, 0)\n",
+    "actual = reported_2008 - reported_2007\n",
+    "\n",
+    "pct_2007 = 1.0 / as_series(diag[\"CDF\"]).to_numpy()\n",
+    "cdf_2008 = np.array([selected_cdf.get(int(age) + 12, 1.000) for age in sheet2[\"Age\"]])\n",
+    "pct_2008 = 1.0 / cdf_2008\n",
+    "\n",
+    "sheet3 = pd.DataFrame(index=years)\n",
+    "sheet3[\"Selected Ultimate\"] = sheet2[\"Projected Ultimate\"]\n",
+    "sheet3[\"% Reported 12/31/07\"] = np.round(pct_2007, 3)\n",
+    "sheet3[\"% Reported 12/31/08\"] = np.round(pct_2008, 3)\n",
+    "sheet3[\"Reported 12/31/07\"] = reported_2007\n",
+    "sheet3[\"Reported 12/31/08\"] = reported_2008\n",
+    "sheet3[\"Actual\"] = actual\n",
+    "sheet3[\"Expected\"] = expected\n",
+    "sheet3[\"Difference\"] = actual - expected\n",
+    "display(sheet3)\n",
+    "display(sheet3[[\"Actual\", \"Expected\", \"Difference\"]].sum().rename(\"Total\").to_frame().T)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "ch15m-sheet4-md",
+   "metadata": {},
+   "source": [
+    "## Exhibit IV, Sheet 4 - Monthly monitoring test\n",
+    "\n",
+    "DC Insurer has quarterly development factors. Monthly percent-reported values\n",
+    "are **linear interpolations of the quarterly percent reported**. Between age 12\n",
+    "(88.0%) and age 15 ($1 / 1.016 \\approx 98.4%$) that gives 91.5% at 13 months\n",
+    "and 95.0% at 14 months, matching the printed January / February 2008 template.\n",
+    "\n",
+    "Expected monthly emergence uses the fitted `ibnr_` and those interpolated\n",
+    "percents: $\\text{IBNR} \\times (p_{t+1} - p_t) / (1 - p_t)$. The quarterly\n",
+    "triangle cannot hold monthly CDFs, so the interpolation stays on the selected\n",
+    "pattern rather than on `DevelopmentConstant`."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "ch15m-sheet4",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "def pct_reported_at(age):\n",
+    "    \"\"\"Linearly interpolate percent reported between quarterly CDF ages.\"\"\"\n",
+    "    knots = np.array(sorted(selected_cdf))\n",
+    "    pcts = 1.0 / np.array([selected_cdf[k] for k in knots])\n",
+    "    if age <= knots[0]:\n",
+    "        return float(pcts[0])\n",
+    "    if age >= knots[-1]:\n",
+    "        return 1.0\n",
+    "    return float(np.interp(age, knots, pcts))\n",
+    "\n",
+    "\n",
+    "pct_jan = np.array([pct_reported_at(age + 1) for age in sheet2[\"Age\"]])\n",
+    "pct_feb = np.array([pct_reported_at(age + 2) for age in sheet2[\"Age\"]])\n",
+    "\n",
+    "# Printed latest reported at 1/31/08 and 2/29/08 for the two immature years.\n",
+    "reported_jan = reported_2007.copy()\n",
+    "reported_feb = reported_2007.copy()\n",
+    "reported_jan.loc[2007] = 2473\n",
+    "reported_feb.loc[2007] = 2538\n",
+    "reported_jan.loc[2006] = 2951\n",
+    "reported_feb.loc[2006] = 2986\n",
+    "\n",
+    "ibnr = as_series(model.ibnr_)\n",
+    "unreported = 1.0 - pct_2007\n",
+    "scale = np.divide(\n",
+    "    ibnr.to_numpy(), unreported, out=np.zeros(len(ibnr)), where=unreported > 0\n",
+    ")\n",
+    "expected_jan = np.round(scale * (pct_jan - pct_2007), 0)\n",
+    "unreported_jan = 1.0 - pct_jan\n",
+    "remaining = reported_jan.to_numpy()\n",
+    "ibnr_jan = sheet2[\"Projected Ultimate\"].to_numpy() - remaining\n",
+    "scale_feb = np.divide(\n",
+    "    ibnr_jan, unreported_jan, out=np.zeros(len(ibnr)), where=unreported_jan > 0\n",
+    ")\n",
+    "expected_feb = np.round(scale_feb * (pct_feb - pct_jan), 0)\n",
+    "\n",
+    "actual_jan = reported_jan - reported_2007\n",
+    "actual_feb = reported_feb - reported_jan\n",
+    "\n",
+    "sheet4 = pd.DataFrame(index=years)\n",
+    "sheet4[\"Selected Ultimate\"] = sheet2[\"Projected Ultimate\"]\n",
+    "sheet4[\"% Reported 12/31/07\"] = np.round(pct_2007, 3)\n",
+    "sheet4[\"% Reported 1/31/08\"] = np.round(pct_jan, 3)\n",
+    "sheet4[\"% Reported 2/29/08\"] = np.round(pct_feb, 3)\n",
+    "sheet4[\"Reported 12/31/07\"] = reported_2007\n",
+    "sheet4[\"Reported 1/31/08\"] = reported_jan\n",
+    "sheet4[\"Reported 2/29/08\"] = reported_feb\n",
+    "sheet4[\"Actual Jan\"] = actual_jan\n",
+    "sheet4[\"Expected Jan\"] = expected_jan\n",
+    "sheet4[\"Diff Jan\"] = actual_jan - expected_jan\n",
+    "sheet4[\"Actual Feb\"] = actual_feb\n",
+    "sheet4[\"Expected Feb\"] = expected_feb\n",
+    "sheet4[\"Diff Feb\"] = actual_feb - expected_feb\n",
+    "display(sheet4)\n",
+    "display(\n",
+    "    sheet4[\n",
+    "        [\n",
+    "            \"Actual Jan\",\n",
+    "            \"Expected Jan\",\n",
+    "            \"Diff Jan\",\n",
+    "            \"Actual Feb\",\n",
+    "            \"Expected Feb\",\n",
+    "            \"Diff Feb\",\n",
+    "        ]\n",
+    "    ]\n",
+    "    .sum()\n",
+    "    .rename(\"Total\")\n",
+    "    .to_frame()\n",
+    "    .T\n",
+    ")"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "ch15m-recon-md",
+   "metadata": {},
+   "source": [
+    "## Reconciliation"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "ch15m-recon",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# Exhibit IV, Sheet 1\n",
+    "sheet1 = tri_2007[tri_2007.development <= 36].to_frame(origin_as_datetime=False)\n",
+    "sheet1.index = [int(getattr(i, \"year\", i)) for i in sheet1.index]\n",
+    "assert sheet1.loc[1997, 3] == 861\n",
+    "assert sheet1.loc[2007, 12] == 2463\n",
+    "assert sheet1.loc[2006, 24] == 2949\n",
+    "\n",
+    "# Exhibit IV, Sheet 2\n",
+    "assert sheet2.loc[2007, \"Projected Ultimate\"] == 2798\n",
+    "assert sheet2.loc[2006, \"Projected Ultimate\"] == 2952\n",
+    "\n",
+    "# Exhibit IV, Sheet 3\n",
+    "assert sheet3.loc[2007, \"% Reported 12/31/07\"] == 0.880\n",
+    "assert sheet3.loc[2007, \"% Reported 12/31/08\"] == 0.999\n",
+    "assert sheet3.loc[2007, \"Expected\"] == 332\n",
+    "assert sheet3.loc[2006, \"Expected\"] == 3\n",
+    "assert sheet3[\"Expected\"].sum() == 335\n",
+    "\n",
+    "# Exhibit IV, Sheet 4 - interpolated percent reported for AY 2007\n",
+    "assert np.isclose(sheet4.loc[2007, \"% Reported 1/31/08\"], 0.915, atol=5e-4)\n",
+    "assert np.isclose(sheet4.loc[2007, \"% Reported 2/29/08\"], 0.950, atol=5e-4)"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.14.4"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}