From ef31e0936e2989eab80b7c725fa78f93108175f3 Mon Sep 17 00:00:00 2001
From: Alex Richert <alexander.richert@noaa.gov>
Date: Tue, 8 Aug 2023 19:05:18 -0700
Subject: [PATCH] Add note to user_guide.md

---
 docs/user_guide.md | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/docs/user_guide.md b/docs/user_guide.md
index eedd779c..28b108a9 100644
--- a/docs/user_guide.md
+++ b/docs/user_guide.md
@@ -33,6 +33,12 @@ in ipolates_mod. The interpolation method is chosen via the first
 argument of these routines (variable IP). Sub-options are set via the
 IPOPT array.
 
+It should be noted that some routines may behave poorly or unpredictably when
+using 4-byte reals (-DBUILD_4=ON). For instance, there is an ATAN2 function
+used for polar stereo grids where for certain grids/coordinates, floating point
+differences between 4-byte output values (~1e-7) can be amplified into
+noticeable differences in output field values.
+
 ### Bilinear Interpolation
 
 Bilinear interpolation is chosen by setting IP=0.