diff --git a/hed/errors/error_messages.py b/hed/errors/error_messages.py
index b5dfb6060..e5e51d7c5 100644
--- a/hed/errors/error_messages.py
+++ b/hed/errors/error_messages.py
@@ -227,6 +227,8 @@ def val_warning_capitalization(tag):
 
 @hed_tag_error(ValidationErrors.UNITS_MISSING, default_severity=ErrorSeverity.WARNING)
 def val_warning_default_units_used(tag, default_unit):
+    if default_unit is None:
+        return f"No unit specified on - '{tag}'.  Multiple default values exist and cannot be inferred"
     return f"No unit specified. Using '{default_unit}' as the default - '{tag}'"
 
 
diff --git a/hed/models/hed_tag.py b/hed/models/hed_tag.py
index 9d470002b..7e579815f 100644
--- a/hed/models/hed_tag.py
+++ b/hed/models/hed_tag.py
@@ -328,7 +328,7 @@ def _calculate_to_canonical_forms(self, hed_schema):
         return tag_issues
 
     def get_stripped_unit_value(self):
-        """ Return the extension portion without units.
+        """ Return the extension divided into value and units, if the units are valid.
 
         Returns:
             stripped_unit_value (str): The extension portion with the units removed.
@@ -345,6 +345,32 @@ def get_stripped_unit_value(self):
 
         return self.extension, None
 
+    def value_as_default_unit(self):
+        """ Returns the value converted to default units if possible.
+
+            Returns None if the units are invalid.(No default unit or invalid)
+
+        Returns:
+            value (float or None): The extension value as default units.
+                                   If there are not default units, returns None.
+
+        Examples:
+            'Duration/300 ms' will return .3
+
+        """
+        tag_unit_classes = self.unit_classes
+        value, _, units = self.extension.rpartition(" ")
+        if not value:
+            stripped_value = units
+            unit = self.default_unit
+        else:
+            stripped_value, unit = self._get_tag_units_portion(tag_unit_classes)
+
+        if stripped_value:
+            if unit.attributes.get("conversionFactor"):
+                conversion_factor = unit.attributes.get("conversionFactor", 1.0)
+                return float(stripped_value) * float(conversion_factor)
+
     @property
     def unit_classes(self):
         """ Return a dict of all the unit classes this tag accepts.
@@ -476,20 +502,19 @@ def get_tag_unit_class_units(self):
 
         return units
 
-    def get_unit_class_default_unit(self):
+    @property
+    def default_unit(self):
         """ Get the default unit class unit for this tag.
 
+            Only a tag with a single unit class can have default units.
         Returns:
-            str: The default unit class unit associated with the specific tag or an empty string.
-
+            unit(UnitEntry or None): the default unit entry for this tag, or None
         """
-        default_unit = ''
         unit_classes = self.unit_classes.values()
-        if unit_classes:
+        if len(unit_classes) == 1:
             first_unit_class_entry = list(unit_classes)[0]
             default_unit = first_unit_class_entry.has_attribute(HedKey.DefaultUnits, return_value=True)
-
-        return default_unit
+            return first_unit_class_entry.units.get(default_unit, None)
 
     def base_tag_has_attribute(self, tag_attribute):
         """ Check to see if the tag has a specific attribute.
@@ -536,8 +561,9 @@ def _get_tag_units_portion(self, tag_unit_classes):
             tag_unit_classes (dict): Dictionary of valid UnitClassEntry objects for this tag.
 
         Returns:
-            stripped_value (str): The value with the units removed.
-
+            stripped_value (str or None): The value with the units removed.
+                                          This is filled in if there are no units as well.
+            unit (UnitEntry or None): The matching unit entry if one is found
         """
         value, _, units = self.extension.rpartition(" ")
         if not units:
@@ -548,12 +574,12 @@ def _get_tag_units_portion(self, tag_unit_classes):
 
             possible_match = self._find_modifier_unit_entry(units, all_valid_unit_permutations)
             if possible_match and not possible_match.has_attribute(HedKey.UnitPrefix):
-                return value, units
+                return value, possible_match
 
             # Repeat the above, but as a prefix
             possible_match = self._find_modifier_unit_entry(value, all_valid_unit_permutations)
             if possible_match and possible_match.has_attribute(HedKey.UnitPrefix):
-                return units, value
+                return possible_match, value
 
         return None, None
 
diff --git a/hed/schema/hed_schema_entry.py b/hed/schema/hed_schema_entry.py
index 2ea635050..797bd2460 100644
--- a/hed/schema/hed_schema_entry.py
+++ b/hed/schema/hed_schema_entry.py
@@ -2,6 +2,8 @@
 from hed.schema.hed_schema_constants import HedKey
 
 import inflect
+import copy
+
 
 pluralize = inflect.engine()
 pluralize.defnoun("hertz", "hertz")
@@ -133,6 +135,20 @@ def get_known_attributes(self):
         return {key: value for key, value in self.attributes.items()
                 if not self._unknown_attributes or key not in self._unknown_attributes}
 
+    # Give a default deep copy that excludes the _section attribute
+    def __deepcopy__(self, memo):
+        # Create a new instance
+        new_obj = self.__class__.__new__(self.__class__)
+        memo[id(self)] = new_obj  # Add the new object to the memo to handle cyclic references
+
+        for k, v in self.__dict__.items():
+            if k != "_section":
+                new_val = copy.deepcopy(v, memo)
+            else:
+                new_val = v
+            setattr(new_obj, k, new_val)
+        return new_obj
+
 
 class UnitClassEntry(HedSchemaEntry):
     """ A single unit class entry in the HedSchema. """
@@ -169,7 +185,11 @@ def finalize_entry(self, schema):
             for derived_unit in new_derivative_units:
                 derivative_units[derived_unit] = unit_entry
                 for modifier in unit_entry.unit_modifiers:
-                    derivative_units[modifier.name + derived_unit] = unit_entry
+                    new_entry = copy.deepcopy(unit_entry)
+                    derivative_units[modifier.name + derived_unit] = new_entry
+                    new_entry.unit_class_name = derived_unit
+                    new_entry.attributes["conversionFactor"] = new_entry.get_conversion_factor(modifier_entry=modifier)
+
         self.derivative_units = derivative_units
 
     def __eq__(self, other):
@@ -182,7 +202,6 @@ def __eq__(self, other):
 
 class UnitEntry(HedSchemaEntry):
     """ A single unit entry with modifiers in the HedSchema. """
-
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
         self.unit_class_name = None
@@ -197,6 +216,19 @@ def finalize_entry(self, schema):
         """
         self.unit_modifiers = schema._get_modifiers_for_unit(self.name)
 
+    def get_conversion_factor(self, modifier_entry):
+        """Returns the conversion factor from combining this unit with the specified modifier
+
+        Parameters:
+            modifier_entry (HedSchemaEntry): The modifier to apply
+
+        Returns:
+            conversion_factor(float): Defaults to 1.0 conversion factor if not present on unit and modifier.
+        """
+        base_factor = float(self.attributes.get("conversionFactor", "1.0").replace("^", "e"))
+        modifier_factor = float(modifier_entry.attributes.get("conversionFactor", "1.0").replace("^", "e"))
+        return base_factor * modifier_factor
+
 
 class HedTagEntry(HedSchemaEntry):
     """ A single tag entry in the HedSchema. """
diff --git a/hed/validator/tag_validator.py b/hed/validator/tag_validator.py
index 586d823da..f0d585a70 100644
--- a/hed/validator/tag_validator.py
+++ b/hed/validator/tag_validator.py
@@ -307,7 +307,7 @@ def _check_units(self, original_tag, bad_units, report_as):
             validation_issue = ErrorHandler.format_error(ValidationErrors.UNITS_INVALID,
                                                          tag=report_as, units=tag_unit_class_units)
         else:
-            default_unit = original_tag.get_unit_class_default_unit()
+            default_unit = original_tag.default_unit
             validation_issue = ErrorHandler.format_error(ValidationErrors.UNITS_MISSING,
                                                          tag=report_as, default_unit=default_unit)
         return validation_issue
@@ -378,26 +378,6 @@ def check_tag_requires_child(self, original_tag):
                                                            tag=original_tag)
         return validation_issues
 
-    def check_tag_unit_class_units_exist(self, original_tag):
-        """ Report warning if tag has a unit class tag with no units.
-
-        Parameters:
-            original_tag (HedTag): The original tag that is used to report the error.
-
-        Returns:
-            list: Validation issues.  Each issue is a dictionary.
-
-        """
-        validation_issues = []
-        if original_tag.is_unit_class_tag():
-            tag_unit_values = original_tag.extension
-            if tag_validator_util.validate_numeric_value_class(tag_unit_values):
-                default_unit = original_tag.get_unit_class_default_unit()
-                validation_issues += ErrorHandler.format_error(ValidationErrors.UNITS_MISSING,
-                                                               tag=original_tag,
-                                                               default_unit=default_unit)
-        return validation_issues
-
     def check_for_invalid_extension_chars(self, original_tag):
         """Report invalid characters in extension/value.
 
diff --git a/readthedocs.yml b/readthedocs.yml
index 3a0eed7e6..bf5d7274d 100644
--- a/readthedocs.yml
+++ b/readthedocs.yml
@@ -5,7 +5,9 @@ formats:
   - pdf
 
 build:
-  image: latest
+  os: "ubuntu-22.04"
+  tools:
+    python: "3.8"
 
 # Build documentation in the docs/ directory with Sphinx
 sphinx:
@@ -15,7 +17,6 @@ sphinx:
 
 
 python:
-  version: 3.8
   install:
    - requirements: docs/requirements.txt
   system_packages: true
diff --git a/tests/models/test_hed_tag.py b/tests/models/test_hed_tag.py
index 50b1e1587..97e0ee247 100644
--- a/tests/models/test_hed_tag.py
+++ b/tests/models/test_hed_tag.py
@@ -1,10 +1,16 @@
 from hed.models.hed_tag import HedTag
 from tests.validator.test_tag_validator_base import TestHedBase
 from hed.schema import HedKey
+from hed import load_schema_version
+
+from tests.schema import util_create_schemas
 
 
 class TestValidatorUtilityFunctions(TestHedBase):
-    schema_file = '../data/schema_tests/HED8.0.0t.xml'
+
+    @classmethod
+    def setUpClass(cls):
+        cls.hed_schema = load_schema_version("8.2.0")
 
     def test_if_tag_exists(self):
         valid_tag1 = HedTag('Left-handed', hed_schema=self.hed_schema)
@@ -37,7 +43,9 @@ def test_if_tag_exists(self):
 
 
 class TestSchemaUtilityFunctions(TestHedBase):
-    schema_file = '../data/schema_tests/HED8.0.0t.xml'
+    @classmethod
+    def setUpClass(cls):
+        cls.hed_schema = load_schema_version("8.2.0")
 
     def test_correctly_determine_tag_takes_value(self):
         value_tag1 = HedTag('Distance/35 px', hed_schema=self.hed_schema)
@@ -65,14 +73,14 @@ def test_should_determine_default_unit(self):
         #                          schema=self.schema)
         no_unit_class_tag = HedTag('RGB-red/0.5', hed_schema=self.hed_schema)
         no_value_tag = HedTag('Black', hed_schema=self.hed_schema)
-        unit_class_tag1_result = unit_class_tag1.get_unit_class_default_unit()
-        # unit_class_tag2_result = unit_class_tag2.get_unit_class_default_unit()
-        no_unit_class_tag_result = no_unit_class_tag.get_unit_class_default_unit()
-        no_value_tag_result = no_value_tag.get_unit_class_default_unit()
-        self.assertEqual(unit_class_tag1_result, 's')
+        unit_class_tag1_result = unit_class_tag1.default_unit
+        # unit_class_tag2_result = unit_class_tag2.default_unit
+        no_unit_class_tag_result = no_unit_class_tag.default_unit
+        no_value_tag_result = no_value_tag.default_unit
+        self.assertEqual(unit_class_tag1_result.name, 's')
         # self.assertEqual(unit_class_tag2_result, '$')
-        self.assertEqual(no_unit_class_tag_result, '')
-        self.assertEqual(no_value_tag_result, '')
+        self.assertEqual(no_unit_class_tag_result, None)
+        self.assertEqual(no_value_tag_result, None)
 
     def test_correctly_determine_tag_unit_classes(self):
         unit_class_tag1 = HedTag('distance/35 px', hed_schema=self.hed_schema)
@@ -97,13 +105,14 @@ def test_determine_tags_legal_units(self):
         unit_class_tag1_result = unit_class_tag1.get_tag_unit_class_units()
         # unit_class_tag2_result = unit_class_tag2.get_tag_unit_class_units()
         no_unit_class_tag_result = no_unit_class_tag.get_tag_unit_class_units()
-        self.assertCountEqual(unit_class_tag1_result, [
+        self.assertCountEqual(sorted(unit_class_tag1_result), sorted([
             'inch',
             'm',
             'foot',
             'metre',
+            'meter',
             'mile',
-        ])
+        ]))
         # self.assertCountEqual(unit_class_tag2_result, [
         #     'dollar',
         #     '$',
@@ -160,4 +169,20 @@ def test_determine_allows_extensions(self):
         self.assertEqual(extension_tag1_result, True)
         self.assertEqual(no_extension_tag1_result, False)
         self.assertEqual(no_extension_tag2_result, False)
-        self.assertEqual(no_extension_tag3_result, False)
\ No newline at end of file
+        self.assertEqual(no_extension_tag3_result, False)
+
+    def test_get_as_default_units(self):
+        tag = HedTag("Duration/300 ms", hed_schema=self.hed_schema)
+        self.assertAlmostEqual(0.3, tag.value_as_default_unit())
+
+        tag2 = HedTag("Duration/300", hed_schema=self.hed_schema)
+        self.assertAlmostEqual(300, tag2.value_as_default_unit())
+
+        tag3 = HedTag("Duration/300 m", hed_schema=self.hed_schema)
+        self.assertEqual(None, tag3.value_as_default_unit())
+
+        tag4 = HedTag("IntensityTakesValue/300", hed_schema=util_create_schemas.load_schema_intensity())
+        self.assertEqual(300, tag4.value_as_default_unit())
+
+        tag5 = HedTag("IntensityTakesValue/300 cd", hed_schema=util_create_schemas.load_schema_intensity())
+        self.assertEqual(None, tag5.value_as_default_unit())
diff --git a/tests/schema/test_schema_compare.py b/tests/schema/test_schema_compare.py
index 6356f67e8..f6b1ceed1 100644
--- a/tests/schema/test_schema_compare.py
+++ b/tests/schema/test_schema_compare.py
@@ -1,54 +1,19 @@
 import unittest
 import json
 
-from hed.schema import HedKey, HedSectionKey, from_string
+from hed.schema import HedKey, HedSectionKey
 from hed.schema.schema_compare import compare_schemas, find_matching_tags, \
     _pretty_print_diff_all, _pretty_print_missing_all, compare_differences
 from hed import load_schema_version
 
+from . import util_create_schemas
 
-class TestSchemaComparison(unittest.TestCase):
-    library_schema_start = """HED library="testcomparison" version="1.1.0" withStandard="8.2.0" unmerged="true"
-
-'''Prologue'''
-
-!# start schema
-
-"""
-
-    library_schema_end = """
-!# end schema
-
-!# end hed
-    """
-
-    def _get_test_schema(self, node_lines):
-        library_schema_string = self.library_schema_start + "\n".join(node_lines) + self.library_schema_end
-        test_schema = from_string(library_schema_string, ".mediawiki")
-
-        return test_schema
-
-    def load_schema1(self):
-        test_nodes = ["'''TestNode''' <nowiki> [This is a simple test node]</nowiki>\n",
-                      " *TestNode2",
-                      " *TestNode3",
-                      " *TestNode4"
-                      ]
-        return self._get_test_schema(test_nodes)
-
-    def load_schema2(self):
-        test_nodes = ["'''TestNode''' <nowiki> [This is a simple test node]</nowiki>\n",
-                      " *TestNode2",
-                      " **TestNode3",
-                      " *TestNode5"
-                      ]
-
-        return self._get_test_schema(test_nodes)
 
+class TestSchemaComparison(unittest.TestCase):
     def test_find_matching_tags(self):
         # create entries for schema1
-        schema1 = self.load_schema1()
-        schema2 = self.load_schema2()
+        schema1 = util_create_schemas.load_schema1()
+        schema2 = util_create_schemas.load_schema2()
 
         result = find_matching_tags(schema1, schema2)
         # Check if the result is correct
@@ -82,8 +47,8 @@ def test_find_matching_tags(self):
         self.assertNotIn("summary", json_style_dict_no_summary)
 
     def test_compare_schemas(self):
-        schema1 = self.load_schema1()
-        schema2 = self.load_schema2()
+        schema1 = util_create_schemas.load_schema1()
+        schema2 = util_create_schemas.load_schema2()
 
         matches, not_in_schema1, not_in_schema2, unequal_entries = compare_schemas(schema1, schema2)
 
@@ -103,8 +68,8 @@ def test_compare_schemas(self):
         self.assertIn("TestNode3", unequal_entries[HedSectionKey.Tags])
 
     def test_compare_differences(self):
-        schema1 = self.load_schema1()
-        schema2 = self.load_schema2()
+        schema1 = util_create_schemas.load_schema1()
+        schema2 = util_create_schemas.load_schema2()
 
         not_in_schema1, not_in_schema2, unequal_entries = compare_differences(schema1, schema2)
 
diff --git a/tests/schema/util_create_schemas.py b/tests/schema/util_create_schemas.py
new file mode 100644
index 000000000..850d014eb
--- /dev/null
+++ b/tests/schema/util_create_schemas.py
@@ -0,0 +1,47 @@
+from hed.schema import HedKey, HedSectionKey, from_string
+
+
+library_schema_start = """HED library="testcomparison" version="1.1.0" withStandard="8.2.0" unmerged="true"
+
+'''Prologue'''
+
+!# start schema
+
+"""
+
+library_schema_end = """
+!# end schema
+
+!# end hed
+    """
+
+def _get_test_schema(node_lines):
+    library_schema_string = library_schema_start + "\n".join(node_lines) + library_schema_end
+    test_schema = from_string(library_schema_string, ".mediawiki")
+
+    return test_schema
+
+
+def load_schema1():
+    test_nodes = ["'''TestNode''' <nowiki> [This is a simple test node]</nowiki>\n",
+                  " *TestNode2",
+                  " *TestNode3",
+                  " *TestNode4"
+                  ]
+    return _get_test_schema(test_nodes)
+
+
+def load_schema2():
+    test_nodes = ["'''TestNode''' <nowiki> [This is a simple test node]</nowiki>\n",
+                  " *TestNode2",
+                  " **TestNode3",
+                  " *TestNode5"
+                  ]
+
+    return _get_test_schema(test_nodes)
+
+
+def load_schema_intensity():
+    test_nodes = ["'''IntensityTakesValue'''",
+                  " * # {unitClass=intensityUnits}"]
+    return _get_test_schema(test_nodes)
\ No newline at end of file