-The data used for updating the RRD was acquired at a certain time. This
-time can either be defined in seconds since 1970-01-01. Or by using the
-letter 'N' the update time is set to be the current time. Negative time
-values are subtracted from the current time.
-An AT_STYLE TIME SPECIFICATION (see the I<rrdfetch> documentation) may
-also be used by delimiting the end of the time specification with the '@' character
-instead of a ':'.
-Getting the timing right to the second is especially
-important when you are working with data-sources of type B<COUNTER>,
-B<DERIVE> or B<ABSOLUTE>.
-
-The remaining elements of the argument are DS updates. The order of this list is
-the same as the order the data sources were defined in the RRA.
-If there is no data for a certain data-source, the letter
-B<U> (e.g., N:0.1:U:1) can be defined.
-
-The format of the value acquired from the data source is dependent of the
-data source type chosen. Normally it will be numeric, but the data acquisition
-modules may impose their very own parsing of this parameter as long as the colon
-(B<:>) remains the data source value separator.
+The data used for updating the RRD was acquired at a certain
+time. This time can either be defined in seconds since 1970-01-01 or
+by using the letter 'N', in which case the update time is set to be
+the current time. Negative time values are subtracted from the current
+time. An AT_STYLE TIME SPECIFICATION (see the I<rrdfetch>
+documentation) may also be used by delimiting the end of the time
+specification with the '@' character instead of a ':'. Getting the
+timing right to the second is especially important when you are
+working with data-sources of type B<COUNTER>, B<DERIVE> or
+B<ABSOLUTE>.
+
+When using negative time values, options and data have to be separated
+by two dashes (B<-->), else the time value would be parsed as an option.
+See below for an example.
+
+When using negative time values, options and data have to be separated
+by two dashes (B<-->), else the time value would be parsed as an option.
+See below for an example.
+
+The remaining elements of the argument are DS updates. The order of
+this list is the same as the order the data sources were defined in
+the RRA. If there is no data for a certain data-source, the letter
+B<U> (e.g., N:0.1:U:1) can be specified.
+
+The format of the value acquired from the data source is dependent on
+the data source type chosen. Normally it will be numeric, but the data
+acquisition modules may impose their very own parsing of this
+parameter as long as the colon (B<:>) remains the data source value
+separator.