From de5e485ed757b6ea8a8c709e79fa98aa4a58e227 Mon Sep 17 00:00:00 2001
From: Scott Lahteine <github@thinkyhead.com>
Date: Wed, 3 May 2017 01:19:44 -0500
Subject: [PATCH] Explicit upward angle solution

---
 Marlin/ubl_G29.cpp | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/Marlin/ubl_G29.cpp b/Marlin/ubl_G29.cpp
index 024ff759b4..b26096a971 100644
--- a/Marlin/ubl_G29.cpp
+++ b/Marlin/ubl_G29.cpp
@@ -1522,10 +1522,8 @@
     if (isnan(ubl.z_values[x][y]) && !isnan(ubl.z_values[x1][y1]) && !isnan(ubl.z_values[x2][y2])) {
       if (ubl.z_values[x1][y1] < ubl.z_values[x2][y2])                  // Angled downward?
         ubl.z_values[x][y] = ubl.z_values[x1][y1];                      // Use nearest (maybe a little too high.)
-      else {
-        const float diff = ubl.z_values[x1][y1] - ubl.z_values[x2][y2]; // Angled upward
-        ubl.z_values[x][y] = ubl.z_values[x1][y1] + diff;               // Use closest plus difference
-      }
+      else
+        ubl.z_values[x][y] = 2.0 * ubl.z_values[x1][y1] - ubl.z_values[x2][y2];   // Angled upward...
       return true;
     }
     return false;