From 5f9d68c8d93b792116fc474cb4ec3072b7baa6f1 Mon Sep 17 00:00:00 2001
From: MatthewFlamm <39341281+MatthewFlamm@users.noreply.github.com>
Date: Fri, 6 May 2022 19:25:44 -0400
Subject: [PATCH] Clarify precision when using NUMBER option in
 --doctest-modules (#9914)

Fix #9892
---
 doc/en/how-to/doctest.rst | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/doc/en/how-to/doctest.rst b/doc/en/how-to/doctest.rst
index 112c9305e..021ba274f 100644
--- a/doc/en/how-to/doctest.rst
+++ b/doc/en/how-to/doctest.rst
@@ -126,14 +126,17 @@ pytest also introduces new options:
   in expected doctest output.
 
 * ``NUMBER``: when enabled, floating-point numbers only need to match as far as
-  the precision you have written in the expected doctest output. For example,
-  the following output would only need to match to 2 decimal places::
+  the precision you have written in the expected doctest output. The numbers are
+  compared using :func:`pytest.approx` with relative tolerance equal to the
+  precision. For example, the following output would only need to match to 2
+  decimal places when comparing ``3.14`` to
+  ``pytest.approx(math.pi, rel=10**-2)``::
 
       >>> math.pi
       3.14
 
-  If you wrote ``3.1416`` then the actual output would need to match to 4
-  decimal places; and so on.
+  If you wrote ``3.1416`` then the actual output would need to match to
+  approximately 4 decimal places; and so on.
 
   This avoids false positives caused by limited floating-point precision, like
   this::