=head2 Time ranges
Last four weeks: --start end-4w --end 00:00
- January 2001: --start 200101010000 --end start+31d
- January 2001: --start 200101010000 --end 200102010000
+ January 2001: --start 20010101 --end start+31d
+ January 2001: --start 20010101 --end 20010201
Last hour: --start end-1h
Last 24 hours: <nothing at all>
Yesterday: --end 00:00
=item B<TICK>B<:>I<vname>B<#>I<rrggbb>[I<aa>][B<:>I<fraction>[B<:>I<legend>]]
Plot a tick mark (a vertical line) for each value of I<vname> that is
-non-zero and not *UNKNOWN*. The I<fraction> argument specifies the
-length of the tick mark as a fraction of the y-axis; the default value
-is 0.1 (10% of the axis). Note that the color specification is not
-optional.
+non-zero and not *UNKNOWN*. The I<fraction> argument specifies the length of
+the tick mark as a fraction of the y-axis; the default value is 0.1 (10% of
+the axis). Note that the color specification is not optional. The TICK marks
+start at y==0 if it is inside the graph. Else they start at the border that
+is closer to 0.
=item B<SHIFT>B<:>I<vname>B<:>I<offset>