diff --git a/docs/source/conf.py b/docs/source/conf.py
index e81d5aa82af..d6d7addb373 100644
--- a/docs/source/conf.py
+++ b/docs/source/conf.py
@@ -465,4 +465,6 @@ def linkcode_resolve(domain, info) -> Optional[str]:  # noqa: ANN001
     "https://jonathan-hui.medium.com/map-mean-average-precision-for-object-detection-45c121a31173",
     # Character Error Rate (site under maintenance see links.rst)
     "https://rechtsprechung-im-ostseeraum.archiv.uni-greifswald.de",
+    # Pearson's Contingency Coefficient (NIST dataplot server intermittently returns 504)
+    "https://www.itl.nist.gov/div898/software/dataplot/refman2/auxillar/pearcont.htm",
 ]