diff --git a/.github/workflows/default-tests.yml b/.github/workflows/default-tests.yml
index ff039fe9..08ee54c6 100644
--- a/.github/workflows/default-tests.yml
+++ b/.github/workflows/default-tests.yml
@@ -9,13 +9,8 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12"]
+        python-version: [ "3.8", "3.9", "3.10", "3.11", "3.12" ]
         os: [windows-latest, ubuntu-latest, macos-latest]
-        experimental: [false]
-        include:
-          - python-version: "3.12"
-            os: "ubuntu-latest"
-            experimental: true
       fail-fast: false
     defaults:
       run:
@@ -35,11 +30,6 @@ jobs:
           --file test_requirements.txt
           --channel conda-forge
 
-    - name: Install unstable dependencies
-      if: matrix.experimental == true
-      run: |
-        micromamba install conda-forge/label/numpy_dev::numpy
-
     - name: Install compliance-checker
       run: |
         python -m pip install -e . --no-deps --force-reinstall
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 7cbe1199..3a3ecd05 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -31,7 +31,7 @@ repos:
 
 
 - repo: https://github.com/astral-sh/ruff-pre-commit
-  rev: v0.4.6
+  rev: v0.5.0
   hooks:
     - id: ruff
 
diff --git a/compliance_checker/cf/cf_1_6.py b/compliance_checker/cf/cf_1_6.py
index d7fa6906..2bf0f74a 100644
--- a/compliance_checker/cf/cf_1_6.py
+++ b/compliance_checker/cf/cf_1_6.py
@@ -925,7 +925,7 @@ def _check_valid_standard_units(self, ds, variable_name):
         # IMPLEMENTATION CONFORMANCE 4.4 REQUIRED 1/2
         elif standard_name == "time":
             valid_standard_units.assert_true(
-                util.units_convertible(units, "seconds since 1970-01-01"),
+                cfutil.units_convertible(units, "seconds since 1970-01-01"),
                 "time must be in a valid units format <unit> since <epoch> "
                 f"not {units}",
             )
@@ -1694,7 +1694,7 @@ def check_dimensional_vertical_coordinate(
                 "there is no default",
             )
 
-            if not util.units_convertible("bar", units):
+            if not cfutil.units_convertible("bar", units):
                 valid_vertical_coord.assert_true(
                     positive in ("up", "down"),
                     f"{name}: vertical coordinates not defining pressure must include "
diff --git a/compliance_checker/cf/util.py b/compliance_checker/cf/util.py
index 591a7b3e..9443eb33 100644
--- a/compliance_checker/cf/util.py
+++ b/compliance_checker/cf/util.py
@@ -9,6 +9,8 @@
 from lxml import etree
 from netCDF4 import Dataset
 
+from compliance_checker.cfutil import units_convertible
+
 # copied from paegan
 # paegan may depend on these later
 _possiblet = {
@@ -325,17 +327,6 @@ def units_known(units):
     return True
 
 
-def units_convertible(units1, units2, reftimeistime=True):
-    """Return True if a Unit representing the string units1 can be converted
-    to a Unit representing the string units2, else False."""
-    try:
-        u1 = Unit(units1)
-        u2 = Unit(units2)
-    except ValueError:
-        return False
-    return u1.is_convertible(u2)
-
-
 def units_temporal(units):
     try:
         u = Unit(units)
diff --git a/compliance_checker/tests/test_cf.py b/compliance_checker/tests/test_cf.py
index 5e13bb7b..3db25d2d 100644
--- a/compliance_checker/tests/test_cf.py
+++ b/compliance_checker/tests/test_cf.py
@@ -29,7 +29,6 @@
     download_cf_standard_name_table,
     is_time_variable,
     is_vertical_coordinate,
-    units_convertible,
     units_temporal,
 )
 from compliance_checker.suite import CheckSuite
@@ -1903,8 +1902,8 @@ def test_check_cell_methods(self):
     # --------------------------------------------------------------------------------
 
     def test_temporal_unit_conversion(self):
-        self.assertTrue(units_convertible("hours", "seconds"))
-        self.assertFalse(units_convertible("hours", "hours since 2000-01-01"))
+        self.assertTrue(cfutil.units_convertible("hours", "seconds"))
+        self.assertFalse(cfutil.units_convertible("hours", "hours since 2000-01-01"))
 
     def test_units_temporal(self):
         self.assertTrue(units_temporal("hours since 2000-01-01"))
diff --git a/pyproject.toml b/pyproject.toml
index 94920af3..9bb30233 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -48,6 +48,7 @@ entry-points."compliance_checker.suites"."acdd-1.3" = "compliance_checker.acdd:A
 entry-points."compliance_checker.suites"."cf-1.6" = "compliance_checker.cf.cf:CF1_6Check"
 entry-points."compliance_checker.suites"."cf-1.7" = "compliance_checker.cf.cf:CF1_7Check"
 entry-points."compliance_checker.suites"."cf-1.8" = "compliance_checker.cf.cf:CF1_8Check"
+entry-points."compliance_checker.suites"."cf-1.9" = "compliance_checker.cf.cf:CF1_9Check"
 entry-points."compliance_checker.suites"."ioos-0.1" = "compliance_checker.ioos:IOOS0_1Check"
 entry-points."compliance_checker.suites"."ioos-1.1" = "compliance_checker.ioos:IOOS1_1Check"
 entry-points."compliance_checker.suites"."ioos-1.2" = "compliance_checker.ioos:IOOS1_2Check"