each day. The labels are placed exactly between two major grid lines
as they specify the complete day and not just midnight.
+[B<--week-fmt> I<strftime format string>]
+
+By default rrdtool uses "Week %V" to render the week number. With this option
+you can define your own format, without completely overriding the xaxis format.
+
=head2 Y-Axis
[B<-y>|B<--y-grid> I<grid step>B<:>I<label factor>]