diff --git a/chainladder/adjustments/disposal.py b/chainladder/adjustments/disposal.py
index fcd3a568f..2e4e3fa06 100644
--- a/chainladder/adjustments/disposal.py
+++ b/chainladder/adjustments/disposal.py
@@ -339,3 +339,28 @@ def fit_transform(self, X, y=None, sample_weight=None):
             Triangle with new full_triangle_
         """
         return self.fit(X, y, sample_weight).transform(X, sample_weight=sample_weight)
+
+    def _param_property(self, X: Triangle, params: np.ndarray) -> Triangle:
+        """
+        Private method to wrap a numpy array into a Triangle
+
+        Uses and overrides DevelopmentBase._param_property.
+
+        Parameters
+        ----------
+        X : Triangle
+            The Triangle object that we want to place the parameter into
+
+        params : np.ndarray
+            The parammeter we want to turn into a Triangle
+
+        Returns
+        -------
+        Triangle
+            A Triangle that mimics X but has params values
+        """
+        obj = super()._param_property(X, params)
+        obj.values = params
+        obj.is_disposal_rate = True
+
+        return obj
diff --git a/chainladder/core/base.py b/chainladder/core/base.py
index ac89fc131..ae20ae43b 100644
--- a/chainladder/core/base.py
+++ b/chainladder/core/base.py
@@ -28,6 +28,7 @@
 from chainladder.utils.sparse import sp
 
 from chainladder.adjustments.disposal import DisposalMixin
+from chainladder.development.incremental import IncrementalMixin
 
 from typing import Optional, TYPE_CHECKING
 
@@ -50,6 +51,7 @@ class TriangleBase(
     Common,
     ABC,
     DisposalMixin,
+    IncrementalMixin,
 ):
     """This class handles the initialization of a triangle"""
 
diff --git a/chainladder/core/common.py b/chainladder/core/common.py
index 8f421cb51..53eee285d 100644
--- a/chainladder/core/common.py
+++ b/chainladder/core/common.py
@@ -82,7 +82,7 @@ def has_ldf(self):
 
     @property
     def has_zeta(self):
-        if hasattr(self, "zeta_"):
+        if hasattr(self, "_zeta_"):
             return True
         else:
             return False
@@ -159,13 +159,6 @@ def pct_unreported_(self):
             )
         return 1 - 1 / self.cdf_
 
-    @property
-    def cum_zeta_(self):
-        if not self.has_zeta:
-            x = self.__class__.__name__
-            raise AttributeError("'" + x + "' object has no attribute 'cum_zeta_'")
-        return self.zeta_.incr_to_cum()
-
     @property
     def ibnr_(self):
         """
diff --git a/chainladder/core/tests/test_triangle.py b/chainladder/core/tests/test_triangle.py
index 45c1e649b..c89ecb00d 100644
--- a/chainladder/core/tests/test_triangle.py
+++ b/chainladder/core/tests/test_triangle.py
@@ -3200,7 +3200,7 @@ def test_has_zeta_true(raa: Triangle) -> None:
     None
     """
     fitted = cl.IncrementalAdditive().fit(raa, sample_weight=raa.latest_diagonal)
-    assert fitted.has_zeta is True
+    assert fitted.has_zeta
 
 
 def test_has_zeta_false(raa: Triangle) -> None:
@@ -3216,7 +3216,7 @@ def test_has_zeta_false(raa: Triangle) -> None:
     -------
     None
     """
-    assert cl.Development().fit(raa).has_zeta is False
+    assert not cl.Development().fit(raa).has_zeta
 
 
 def test_cum_zeta_raises_when_no_zeta(raa: Triangle) -> None:
diff --git a/chainladder/core/triangle.py b/chainladder/core/triangle.py
index a496d7edc..ade43f467 100644
--- a/chainladder/core/triangle.py
+++ b/chainladder/core/triangle.py
@@ -1046,6 +1046,17 @@ def is_disposal_rate(self) -> bool:
     def is_disposal_rate(self, is_dr: bool) -> None:
         self._is_disposal_rate = is_dr
 
+    @property
+    def is_additive(self) -> bool:
+        """
+        Indicates whether the Triangle holds a normal additive ratio (which goes from tail to head)
+        """
+        return getattr(self, "_is_additive", False)
+
+    @is_additive.setter
+    def is_additive(self, is_add: bool) -> None:
+        self._is_additive = is_add
+
     def align_pattern(
         self, X: Triangle, sample_weight: Triangle | None = None
     ) -> Triangle:
@@ -1377,20 +1388,30 @@ def incr_to_cum(self, inplace=False):
         if inplace:
             xp = self.get_array_module()
             if not self.is_cumulative:
-                if self.is_pattern & (not self.is_disposal_rate):
-                    if hasattr(self, "is_additive") and self.is_additive:
-                        values = xp.nan_to_num(self.values[..., ::-1])
-                        values = num_to_value(values, 0)
-                        self.values = (
-                            xp.cumsum(values, -1)[..., ::-1] * self.nan_triangle
-                        )
-                    else:
-                        values = xp.nan_to_num(self.values[..., ::-1])
-                        values = num_to_value(values, 1)
-                        values = xp.cumprod(values, -1)[..., ::-1]
-                        self.values = values * self.nan_triangle
-                        values = num_to_value(values, self.get_array_module(values).nan)
-                else:
+                # fmt: off
+                if (
+                    self.is_pattern
+                    and (not self.is_additive)
+                    and (not self.is_disposal_rate)
+                ):  # for multiplicative ldf triangles (mult from left to right)
+                    # fmt: on
+                    values = xp.nan_to_num(self.values[..., ::-1])
+                    values = num_to_value(values, 1)
+                    values = xp.cumprod(values, -1)[..., ::-1]
+                    self.values = values * self.nan_triangle
+                    values = num_to_value(values, self.get_array_module(values).nan)
+                    # fmt: off
+                elif (
+                    self.is_pattern
+                    and self.is_additive
+                    and (not self.is_disposal_rate)
+                ):  # for additive factor triangles (sum from left to right)
+                    # fmt: on
+                    values = xp.nan_to_num(self.values[..., ::-1])
+                    values = num_to_value(values, 0)
+                    self.values = (xp.cumsum(values, -1)[..., ::-1] * self.nan_triangle)
+                else:  # for normal value triangles 
+                    # also for disposal rate triangles (sum from right to left)
                     if self.array_backend not in ["sparse", "dask"]:
                         self.values = (
                             xp.cumsum(xp.nan_to_num(self.values), 3)
@@ -1466,7 +1487,13 @@ def cum_to_incr(self, inplace=False):
         if inplace:
             v = self.valuation_date
             if self.is_cumulative or self.is_cumulative is None:
-                if self.is_pattern & (not self.is_disposal_rate):
+                # fmt: off
+                if (
+                    self.is_pattern
+                    and (not self.is_additive)
+                    and (not self.is_disposal_rate)
+                ):  # for multiplicative ldf triangles (div from left to right)
+                    # fmt: on
                     xp = self.get_array_module()
                     self.values = num_to_value(xp.nan_to_num(self.values), 1)
                     diff = self.iloc[..., :-1] / self.iloc[..., 1:].values
@@ -1478,7 +1505,17 @@ def cum_to_incr(self, inplace=False):
                         axis=3,
                     )
                     self.values = self.values * self.nan_triangle
-                else:
+                    # fmt: fn
+                elif (
+                    self.is_pattern
+                    and self.is_additive
+                    and (not self.is_disposal_rate)
+                ):  # for additive factor triangles (diff from left to right)
+                    # fmt: on
+                    diff = self.iloc[..., :-1] - self.iloc[..., 1:].values
+                    self = concat((diff, self.iloc[..., -1]), axis=3)
+                else:  # for normal value triangles 
+                    # also for disposal rate triangles (diff from right to left)
                     diff = self.iloc[..., 1:] - self.iloc[..., :-1].values
                     self = concat((self.iloc[..., 0], diff), axis=3)
                 self.is_cumulative = False
diff --git a/chainladder/development/base.py b/chainladder/development/base.py
index 922c4dbc2..4c09067da 100644
--- a/chainladder/development/base.py
+++ b/chainladder/development/base.py
@@ -409,11 +409,8 @@ def _param_property(X: Triangle, params: np.ndarray) -> Triangle:
         from chainladder import options
 
         obj: Triangle = X[X.origin == X.origin.min()]
-        obj.values = params
         obj.valuation_date = pd.to_datetime(options.ULT_VAL)
         obj.is_pattern = True
-        obj.is_additive = True
-        obj.is_cumulative = False
         obj.virtual_columns.columns = {}
         obj._set_slicers()
         return obj
diff --git a/chainladder/development/development.py b/chainladder/development/development.py
index 705e955fe..3559d65cd 100644
--- a/chainladder/development/development.py
+++ b/chainladder/development/development.py
@@ -4,7 +4,6 @@
 from __future__ import annotations
 
 import numpy as np
-import pandas as pd
 import warnings
 
 from chainladder.development.base import DevelopmentBase
@@ -482,16 +481,28 @@ def transform(self, X):
         return X_new
 
     def _param_property(self, X, params, idx):
-        from chainladder import options
+        """
+        Private method to wrap a numpy array into a Triangle
+
+        Uses and overrides DevelopmentBase._param_property.
+
+        Parameters
+        ----------
+        X : Triangle
+            The Triangle object that we want to place the parameter into
+
+        params : np.ndarray
+            The parammeter we want to turn into a Triangle
 
-        obj = X[X.origin == X.origin.min()]
+        Returns
+        -------
+        Triangle
+            A Triangle that mimics X but has params values
+        """
+        obj = super()._param_property(X, params)
         xp = X.get_array_module()
         obj.values = xp.ones(obj.shape)[..., :-1] * params[..., idx : idx + 1, :]
         obj.ddims = X.link_ratio.ddims
-        obj.valuation_date = pd.to_datetime(options.ULT_VAL)
-        obj.is_pattern = True
         obj.is_cumulative = False
-        obj.virtual_columns.columns = {}
-        obj._set_slicers()
 
         return obj
diff --git a/chainladder/development/incremental.py b/chainladder/development/incremental.py
index 0d7195af3..1b2386deb 100644
--- a/chainladder/development/incremental.py
+++ b/chainladder/development/incremental.py
@@ -1,13 +1,66 @@
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at https://mozilla.org/MPL/2.0/.
+from __future__ import annotations
+
 from chainladder.development import DevelopmentBase
 from chainladder.utils import TriangleWeight
 import numpy as np
+import copy
 import warnings
 
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from chainladder.core import Triangle
 
-class IncrementalAdditive(DevelopmentBase):
+
+class IncrementalMixin:
+    """
+    This class provides attributes for the IncrementalAdditive development method
+    and transformed `Triangle`
+    """
+
+    @property
+    def zeta_(self) -> Triangle:
+        """
+        Gets the estimated incremental additive factors
+        """
+        if not hasattr(self, "_zeta_"):
+            raise AttributeError("`zeta_` has not been estimated.")
+        return self._zeta_
+
+    @zeta_.setter
+    def zeta_(self, value: Triangle) -> None:
+        """
+        Sets zeta_
+        """
+        obj = copy.deepcopy(value)
+        obj.is_pattern = True
+        obj.is_additive = True
+        obj.is_cumulative = False
+        self._zeta_ = obj
+
+    @property
+    def cum_zeta_(self) -> Triangle:
+        """
+        Gets the estimated cumulative additive factors
+        """
+        return self.zeta_.incr_to_cum()
+
+    @cum_zeta_.setter
+    def cum_zeta_(self, value: Triangle) -> None:
+        """
+        Sets cum_zeta_
+        """
+        obj = copy.deepcopy(value)
+        obj.is_pattern = True
+        obj.is_additive = True
+        obj.is_cumulative = True
+        self._zeta_ = obj.cum_to_incr()
+
+
+class IncrementalAdditive(DevelopmentBase, IncrementalMixin):
     """
     The Incremental Additive Method.
 
@@ -311,7 +364,7 @@ def transform(self, X):
         for item in [
             "ldf_",
             "w_",
-            "zeta_",
+            "_zeta_",
             "incremental_",
             "tri_zeta",
             "fit_zeta_",
@@ -319,3 +372,28 @@ def transform(self, X):
         ]:
             X_new.__dict__[item] = self.__dict__[item]
         return X_new
+
+    def _param_property(self, X, params):
+        """
+        Private method to wrap a numpy array into a Triangle
+
+        Uses and overrides DevelopmentBase._param_property.
+
+        Parameters
+        ----------
+        X : Triangle
+            The Triangle object that we want to place the parameter into
+
+        params : np.ndarray
+            The parammeter we want to turn into a Triangle
+
+        Returns
+        -------
+        Triangle
+            A Triangle that mimics X but has params values
+        """
+        obj = super()._param_property(X, params)
+        obj.values = params
+        obj.is_additive = True
+
+        return obj
diff --git a/chainladder/development/tests/test_incremental.py b/chainladder/development/tests/test_incremental.py
index 58c6ed3c1..6ff4aa0fe 100644
--- a/chainladder/development/tests/test_incremental.py
+++ b/chainladder/development/tests/test_incremental.py
@@ -1,7 +1,14 @@
+from __future__ import annotations
+
 import chainladder as cl
 import numpy as np
 import pytest
 
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from chainladder.core import Triangle
+
 
 def test_schmidt():
     tri = cl.load_sample("ia_sample")
@@ -90,3 +97,42 @@ def test_pipeline():
     assert np.array_equal(
         dev1.zeta_.values, dev2.named_steps.drop_hilo.zeta_.values, True
     )
+
+
+def test_setting_cum(atol: float) -> None:
+    """
+    IncrementalMixin allows setting cumulative zeta. Validating that the setting function works properly.
+
+    Parameters
+    ----------
+    atol: float
+        the absolute tolerance for this test
+
+    Returns
+    -------
+    None
+    """
+    tri = cl.load_sample("ia_sample")
+    ia = cl.IncrementalAdditive().fit(
+        tri.iloc[0, 0], sample_weight=tri.iloc[0, 1].latest_diagonal
+    )
+    orig_zeta_ = ia.zeta_
+    ia.cum_zeta_ = ia.cum_zeta_ * 2
+    assert np.allclose(ia.zeta_.values, (orig_zeta_ * 2).values, atol=atol)
+
+
+def test_no_zeta(raa: Triangle) -> None:
+    """
+    calling zeta_ on a Triangle without _zeta_ raises
+
+    Parameters
+    ----------
+    raa: Triangle
+        the RAA sample dataset
+
+    Returns
+    -------
+    None
+    """
+    with pytest.raises(AttributeError, match="has not been estimated"):
+        _ = raa.zeta_