diff --git a/doc/content-for-reference.html b/doc/content-for-reference.html
index 4f4535d45..a296cce90 100644
--- a/doc/content-for-reference.html
+++ b/doc/content-for-reference.html
@@ -457,6 +457,10 @@ plotting; here’s a screenshot.
 <img src="data/linreg-example.jpg"/>
 </center>
 
+(Perhaps surprisingly, the fit line doesn&rsquo;t have slope 1. This appears to
+be due to Miller&rsquo;s doing RMS minimization of vertical residuals; a PCA
+analysis gives slope 1 on the dominant eigenvector &mdash; thanks Drew Kunas for
+a good conversation!)
 
 <!-- ================================================================ -->
 <h2>step</h2>
diff --git a/doc/reference.html b/doc/reference.html
index 5f114bd57..c45103d1b 100644
--- a/doc/reference.html
+++ b/doc/reference.html
@@ -1196,6 +1196,10 @@ plotting; here&rsquo;s a screenshot.
 <img src="data/linreg-example.jpg"/>
 </center>
 
+(Perhaps surprisingly, the fit line doesn&rsquo;t have slope 1. This appears to
+be due to Miller&rsquo;s doing RMS minimization of vertical residuals; a PCA
+analysis gives slope 1 on the dominant eigenvector &mdash; thanks Drew Kunas for
+a good conversation!)
 
 <!-- ================================================================ -->
 <h2>step</h2>  <a id="step"/>