added explanation on the rows returned from fetch. fix for #291.

[rrdtool.git] / doc / rrdtutorial.pod

diff --git a/doc/rrdtutorial.pod b/doc/rrdtutorial.pod
index f5ab0f3..e29cd50 100644 (file)
--- a/doc/rrdtutorial.pod
+++ b/doc/rrdtutorial.pod
@@ -323,13 +323,18 @@ It should return the following output:
  920808600: 6.6666666667e-03
  920808900: 3.3333333333e-03
  920809200: nan
-
-If it doesn't, something may be wrong.  Perhaps your OS will print
-"NaN" in a different form. "NaN" stands for "Not A Number".  If your OS
-writes "U" or "UNKN" or something similar that's okay.  If something
-else is wrong, it will probably be due to an error you made (assuming
-that my tutorial is correct of course :-). In that case: delete the
-database and try again. 
+ 920809500: nan 
+
+Note that you might get more rows than you expect. The reason for this is
+that you ask for a time range that ends on 920809200. The number that is
+written behind 920809200: in the list above covers the time range from
+920808900 to 920809200, EXCLUDING 920809200. Hence to be on the sure side,
+you receive the entry from 920809200 to 920809500 as well since it INCLUDES
+920809200. You may also see "NaN" instead of "nan" this is OS dependent.
+"NaN" stands for "Not A Number".  If your OS writes "U" or "UNKN" or
+something similar that's okay.  If something else is wrong, it will probably
+be due to an error you made (assuming that my tutorial is correct of course
+:-). In that case: delete the database and try again.
 
 
 The meaning of the above output will become clear below.