diff --git a/event_model/documents/event_descriptor.py b/event_model/documents/event_descriptor.py
index 3fa799a9..2edb99eb 100644
--- a/event_model/documents/event_descriptor.py
+++ b/event_model/documents/event_descriptor.py
@@ -1,4 +1,4 @@
-from typing import Any, Dict, List, Optional
+from typing import Any, Dict, List
 
 from typing_extensions import Annotated, Literal, NotRequired, TypedDict
 
@@ -41,7 +41,7 @@ class DataKey(TypedDict):
     ]
     precision: NotRequired[
         Annotated[
-            Optional[int],
+            int,
             Field(
                 description="Number of digits after decimal place if "
                 "a floating point number"
@@ -56,7 +56,7 @@ class DataKey(TypedDict):
         str, Field(description="The source (ex piece of hardware) of the data.")
     ]
     units: NotRequired[
-        Annotated[Optional[str], Field(description="Engineering units of the value")]
+        Annotated[str, Field(description="Engineering units of the value")]
     ]
 
 
diff --git a/event_model/schemas/datum_page.json b/event_model/schemas/datum_page.json
index a09dc59f..7d34f988 100644
--- a/event_model/schemas/datum_page.json
+++ b/event_model/schemas/datum_page.json
@@ -14,11 +14,7 @@
     "properties": {
         "datum_id": {
             "description": "Array unique identifiers for each Datum (akin to 'uid' for other Document types), typically formatted as '<resource>/<integer>'",
-            "allOf": [
-                {
-                    "$ref": "#/$defs/DataFrameForDatumPage"
-                }
-            ]
+            "$ref": "#/$defs/DataFrameForDatumPage"
         },
         "datum_kwargs": {
             "title": "Datum Kwargs",
diff --git a/event_model/schemas/event_descriptor.json b/event_model/schemas/event_descriptor.json
index 3549af5f..0c1bf012 100644
--- a/event_model/schemas/event_descriptor.json
+++ b/event_model/schemas/event_descriptor.json
@@ -66,14 +66,7 @@
                 "precision": {
                     "title": "Precision",
                     "description": "Number of digits after decimal place if a floating point number",
-                    "anyOf": [
-                        {
-                            "type": "integer"
-                        },
-                        {
-                            "type": "null"
-                        }
-                    ]
+                    "type": "integer"
                 },
                 "shape": {
                     "title": "Shape",
@@ -91,14 +84,7 @@
                 "units": {
                     "title": "Units",
                     "description": "Engineering units of the value",
-                    "anyOf": [
-                        {
-                            "type": "string"
-                        },
-                        {
-                            "type": "null"
-                        }
-                    ]
+                    "type": "string"
                 }
             },
             "required": [
diff --git a/event_model/schemas/event_page.json b/event_model/schemas/event_page.json
index 55cf9c23..7c987427 100644
--- a/event_model/schemas/event_page.json
+++ b/event_model/schemas/event_page.json
@@ -32,11 +32,7 @@
     "properties": {
         "data": {
             "description": "The actual measurement data",
-            "allOf": [
-                {
-                    "$ref": "#/$defs/DataFrameForEventPage"
-                }
-            ]
+            "$ref": "#/$defs/DataFrameForEventPage"
         },
         "descriptor": {
             "title": "Descriptor",
@@ -45,11 +41,7 @@
         },
         "filled": {
             "description": "Mapping each of the keys of externally-stored data to an array containing the boolean False, indicating that the data has not been loaded, or to foreign keys (moved here from 'data' when the data was loaded)",
-            "allOf": [
-                {
-                    "$ref": "#/$defs/DataFrameForFilled"
-                }
-            ]
+            "$ref": "#/$defs/DataFrameForFilled"
         },
         "seq_num": {
             "title": "Seq Num",
@@ -69,11 +61,7 @@
         },
         "timestamps": {
             "description": "The timestamps of the individual measurement data",
-            "allOf": [
-                {
-                    "$ref": "#/$defs/DataFrameForEventPage"
-                }
-            ]
+            "$ref": "#/$defs/DataFrameForEventPage"
         },
         "uid": {
             "title": "Uid",
diff --git a/event_model/schemas/run_start.json b/event_model/schemas/run_start.json
index e7c019f1..852e44b1 100644
--- a/event_model/schemas/run_start.json
+++ b/event_model/schemas/run_start.json
@@ -72,11 +72,7 @@
                 "calculation": {
                     "title": "calculation properties",
                     "description": "required fields if type is calculated",
-                    "allOf": [
-                        {
-                            "$ref": "#/$defs/Calculation"
-                        }
-                    ]
+                    "$ref": "#/$defs/Calculation"
                 },
                 "config_device": {
                     "title": "Config Device",
@@ -289,11 +285,7 @@
         },
         "data_type": {
             "description": "",
-            "allOf": [
-                {
-                    "$ref": "#/$defs/DataType"
-                }
-            ]
+            "$ref": "#/$defs/DataType"
         },
         "group": {
             "title": "Group",
diff --git a/event_model/schemas/run_stop.json b/event_model/schemas/run_stop.json
index 89f51815..b0d64458 100644
--- a/event_model/schemas/run_stop.json
+++ b/event_model/schemas/run_stop.json
@@ -10,11 +10,7 @@
     "properties": {
         "data_type": {
             "description": "data_type",
-            "allOf": [
-                {
-                    "$ref": "#/$defs/DataType"
-                }
-            ]
+            "$ref": "#/$defs/DataType"
         },
         "exit_status": {
             "title": "Exit Status",
diff --git a/event_model/schemas/stream_datum.json b/event_model/schemas/stream_datum.json
index d5217f39..75b53ed7 100644
--- a/event_model/schemas/stream_datum.json
+++ b/event_model/schemas/stream_datum.json
@@ -33,19 +33,11 @@
         },
         "indices": {
             "description": "A slice object passed to the StreamResource handler so it can hand back data and timestamps",
-            "allOf": [
-                {
-                    "$ref": "#/$defs/StreamRange"
-                }
-            ]
+            "$ref": "#/$defs/StreamRange"
         },
         "seq_nums": {
             "description": "A slice object showing the Event numbers the resource corresponds to",
-            "allOf": [
-                {
-                    "$ref": "#/$defs/StreamRange"
-                }
-            ]
+            "$ref": "#/$defs/StreamRange"
         },
         "stream_resource": {
             "title": "Stream Resource",
diff --git a/event_model/tests/test_em.py b/event_model/tests/test_em.py
index 15e0fd81..015072f2 100644
--- a/event_model/tests/test_em.py
+++ b/event_model/tests/test_em.py
@@ -56,7 +56,7 @@ def test_compose_run():
     assert bundle.compose_stop is compose_stop
     bundle = compose_descriptor(
         data_keys={
-            "motor": {"shape": [], "dtype": "number", "source": "...", "units": None},
+            "motor": {"shape": [], "dtype": "number", "source": "...", "units": "s"},
             "image": {
                 "shape": [512, 512],
                 "dtype": "number",