Flip deflection sign for hooke.driver.wtk.

We want +deflection for +chain tension.

diff --git a/hooke/driver/wtk.py b/hooke/driver/wtk.py
index 46bf92e5c57a0a73cd674e71c4e6340a73ece08e..640f056b92adf652fd3fc4af10b77c5638c3b369 100644 (file)
--- a/hooke/driver/wtk.py
+++ b/hooke/driver/wtk.py
@@ -185,7 +185,11 @@ class WTKDriver (Driver):
             * info['z piezo sensitivity (m/V)']
             )
 
-        ret[:,d_scol] = (
+        # 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_scol] = -(
             (data[:,d_rcol]
              * info['deflection sensitivity (V/bit)']
              - info['deflection offset (V)'])