From e56cff18ed60dc8867d85f5690aca41c4b1b5546 Mon Sep 17 00:00:00 2001
From: "W. Trevor King" <wking@tremily.us>
Date: Thu, 12 Jul 2012 18:25:53 -0400
Subject: [PATCH] Add explanatory message to analyze_surface_position_data's
 final==start error.

---
 pypiezo/surface.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

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
-- 
2.26.2