From 1784c60782f2a15dc9a19c1355bf763680c533fd Mon Sep 17 00:00:00 2001
From: "W. Trevor King" <wking@drexel.edu>
Date: Thu, 3 Jun 2010 10:07:11 -0400
Subject: [PATCH] Flip deflection sign in picoforce driver so +deflection for
 +tension

---
 hooke/driver/picoforce.py | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/hooke/driver/picoforce.py b/hooke/driver/picoforce.py
index c1139d6..178574e 100644
--- a/hooke/driver/picoforce.py
+++ b/hooke/driver/picoforce.py
@@ -343,7 +343,11 @@ class PicoForceDriver (Driver):
             * info['z piezo sensitivity (m/V)']
             )
 
-        ret[:,d_col] = (
+        # Leading '-' because deflection voltage increases as the tip
+        # moves away from the surface, but it makes more sense to me
+        # to have it increase as it moves toward the surface (positive
+        # tension on the protein chain).
+        ret[:,d_col] = -(
             (data[:,d_col]
              * info['deflection sensitivity (V/bit)']
              - info['deflection offset (V)'])
-- 
2.26.2