From: W. Trevor King <wking@tremily.us>
Date: Thu, 12 Jul 2012 22:25:53 +0000 (-0400)
Subject: Add explanatory message to analyze_surface_position_data's final==start error.
X-Git-Tag: 0.7~1
X-Git-Url: http://git.tremily.us/?a=commitdiff_plain;h=e56cff18ed60dc8867d85f5690aca41c4b1b5546;p=pypiezo.git

Add explanatory message to analyze_surface_position_data's final==start error.
---

diff --git a/pypiezo/surface.py b/pypiezo/surface.py
index a0f9055..fe096bb 100644
--- a/pypiezo/surface.py
+++ b/pypiezo/surface.py
@@ -177,7 +177,7 @@ def analyze_surface_position_data(
     start_pos = data['z'].min()
     final_pos = data['z'].max()
     if final_pos == start_pos:
-        raise SurfaceError()
+        raise SurfaceError('cannot fit a single approach step (too close?)')
     start_def = data['deflection'].min()
     final_def = data['deflection'].max()
     # start_def and start_pos are probably for 2 different points