diff --git a/pvlib/clearsky.py b/pvlib/clearsky.py
index 75f598baeb..8c57214800 100644
--- a/pvlib/clearsky.py
+++ b/pvlib/clearsky.py
@@ -687,7 +687,7 @@ def detect_clearsky(measured, clearsky, times, window_length,
         raise NotImplementedError('algorithm does not yet support unequal ' \
                                   'times. consider resampling your data.')
 
-    samples_per_window = int(window_length / sample_interval)
+    samples_per_window = int(window_length / sample_interval) + 1
 
     # generate matrix of integers for creating windows with indexing
     from scipy.linalg import hankel
@@ -697,25 +697,27 @@ def detect_clearsky(measured, clearsky, times, window_length,
     # calculate measurement statistics
     meas_mean = np.mean(measured[H], axis=0)
     meas_max = np.max(measured[H], axis=0)
-    meas_slope = np.diff(measured[H], n=1, axis=0)
+    meas_ghi_diff = np.diff(measured[H], n=1, axis=0)
+    meas_slope = np.diff(measured[H], n=1, axis=0) / sample_interval
     # matlab std function normalizes by N-1, so set ddof=1 here
     meas_slope_nstd = np.std(meas_slope, axis=0, ddof=1) / meas_mean
-    meas_slope_max = np.max(np.abs(meas_slope), axis=0)
+    # meas_slope_max = np.max(np.abs(meas_slope), axis=0)
     meas_line_length = np.sum(np.sqrt(
-        meas_slope*meas_slope + sample_interval*sample_interval), axis=0)
+        meas_ghi_diff*meas_ghi_diff + sample_interval*sample_interval), axis=0)
 
     # calculate clear sky statistics
     clear_mean = np.mean(clearsky[H], axis=0)
     clear_max = np.max(clearsky[H], axis=0)
-    clear_slope = np.diff(clearsky[H], n=1, axis=0)
-    clear_slope_max = np.max(np.abs(clear_slope), axis=0)
+    clear_ghi_diff = np.diff(clearsky[H], n=1, axis=0)
+    clear_slope = np.diff(clearsky[H], n=1, axis=0) / sample_interval
+    # clear_slope_max = np.max(np.abs(clear_slope), axis=0)
 
     from scipy.optimize import minimize_scalar
 
     alpha = 1
     for iteration in range(max_iterations):
         clear_line_length = np.sum(np.sqrt(
-            alpha*alpha*clear_slope*clear_slope +
+            alpha*alpha*clear_ghi_diff*clear_ghi_diff +
             sample_interval*sample_interval), axis=0)
 
         line_diff = meas_line_length - clear_line_length
@@ -725,7 +727,7 @@ def detect_clearsky(measured, clearsky, times, window_length,
         c2 = np.abs(meas_max - alpha*clear_max) < max_diff
         c3 = (line_diff > lower_line_length) & (line_diff < upper_line_length)
         c4 = meas_slope_nstd < var_diff
-        c5 = (meas_slope_max - alpha*clear_slope_max) < slope_dev
+        c5 = np.max(np.abs(meas_slope - alpha*clear_slope), axis=0) < slope_dev
         c6 = (clear_mean != 0) & ~np.isnan(clear_mean)
         clear_windows = c1 & c2 & c3 & c4 & c5 & c6
 
@@ -761,6 +763,13 @@ def rmse(alpha):
         components['slope_max'] = c5
         components['mean_nan'] = c6
         components['windows'] = clear_windows
+
+        components['mean_diff_array'] = np.abs(meas_mean - alpha*clear_mean)
+        components['max_diff_array'] = np.abs(meas_max - alpha*clear_max)
+        components['line_length_array'] = meas_line_length - clear_line_length
+        components['slope_nstd_array'] = meas_slope_nstd
+        components['slope_max_array'] = (np.max(meas_slope - alpha*clear_slope, axis=0))
+
         return clear_samples, components, alpha
     else:
         return clear_samples