diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index c10a5b3..a742812 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -33,12 +33,8 @@ permissions:
   contents: read
 
 jobs:
-  buid-and-test:
-    runs-on: ubuntu-24.04
-
-    strategy:
-      fail-fast: false
-
+  code-health:
+    runs-on:  ubuntu-24.04
     steps:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4
 
@@ -66,6 +62,26 @@ jobs:
 
       - name: Check modified protos
         run: ci/build_changed_protos.sh origin/main
+  
+  build-and-test-correctness:
+    strategy:
+      fail-fast: false
+      matrix:
+        os: ["ubuntu-24.04", "ubuntu-24.04-arm", "macos-13", "macos-14"]
+
+    runs-on: ${{ matrix.os }}
+
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4
+
+      - name: Set up Python 3.12
+        uses: actions/setup-python@3542bca2639a428e1796aaa6a2ffef0c0f575566 # v3
+        with:
+          python-version: '3.12'
+
+      - name: Install Dependencies
+        run: |
+          pip install -r dev_tools/dev.env.txt
 
         #
         # Install
@@ -75,14 +91,40 @@ jobs:
         run: |
           pip install . --user
 
-
       - name: pytest
         run: ci/pytest_unit.sh
 
-      - name: test performance
-        run: ci/pytest_perf.sh
-
       - name: test compatibility with Cirq
         run: |
           pip install cirq-core
           pytest test/* -m cirq
+
+
+  build-and-test-performance:
+    strategy:
+      fail-fast: false
+
+    runs-on: ubuntu-24.04
+
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4
+
+      - name: Set up Python 3.12
+        uses: actions/setup-python@3542bca2639a428e1796aaa6a2ffef0c0f575566 # v3
+        with:
+          python-version: '3.12'
+
+      - name: Install Dependencies
+        run: |
+          pip install -r dev_tools/dev.env.txt
+
+        #
+        # Install
+        #
+
+      - name: install
+        run: |
+          pip install . --user
+
+      - name: test performance
+        run: ci/pytest_perf.sh
diff --git a/test_perf/test_value_performance.py b/test_perf/test_value_performance.py
index 47c8e21..38a7c49 100644
--- a/test_perf/test_value_performance.py
+++ b/test_perf/test_value_performance.py
@@ -74,7 +74,7 @@ def test_perf_repr(a: Value) -> str:
     return repr(a)
 
 
-@perf_goal(avg_nanos=830)
+@perf_goal(avg_nanos=850)
 def test_perf_parse_atom() -> Value:
     return Value(1, 'kilogram')
 
diff --git a/tunits/core/cython/frac.pyx b/tunits/core/cython/frac.pyx
index 79406f7..08d7d84 100644
--- a/tunits/core/cython/frac.pyx
+++ b/tunits/core/cython/frac.pyx
@@ -15,7 +15,6 @@
 cimport cython
 from libc.math cimport floor as c_floor, pow as c_pow
 
-
 # A ratio that should always be canonicalized into least terms with the sign
 # on the numerator.
 cdef struct frac:
@@ -85,10 +84,10 @@ cpdef frac float_to_twelths_frac(a) except *:
         return frac_least_terms(a, 1)
 
     cdef double d = float(a)
-    cdef long long x = <long long>c_floor(12*d + 0.5)
-    if abs(12*d - x) > 1e-5:
-        raise ValueError("Not a twelfth.")
-
+    cdef double raised_d = 12.0*d
+    cdef long long x = <long long>c_floor(raised_d + 0.5)
+    if not (-1e-5 < raised_d - x < 1e-5):
+        raise ValueError(f"{a} with 12*a={raised_d} Not a twelfth.")
     return frac_least_terms(x, 12)