=include name
-=head1 SYNOPSYS
+=head1 SYNOPSIS
I<E<lt>RPN expressionE<gt>> :=
I<E<lt>vnameE<gt>>|I<E<lt>operatorE<gt>>|I<E<lt>valueE<gt>>
B<LT, LE, GT, GE, EQ, NE>
-I<Note: NE is not yet implemented>
-
Pop two elements from the stack, compare them for the selected condition
and return 1 for true or 0 for false. Comparing an I<unknown> or an
I<infinite> value will always result in 0 (false).
B<UN, ISINF>
-I<Note: ISINF is not yet implemented>
-
Pop one element from the stack, compare this to I<unknown> respectively
to I<positive or negative infinity>. Returns 1 for true or 0 for false.
Sine, cosine (input in radians), log, exp (natural logarithm)
+B<ATAN>
+
+Arctangent. Output in radians.
+
B<FLOOR, CEIL>
Round down,up to the nearest integer
step. This allows you to do calculations across the data. This
function cannot be used in B<VDEF> instructions.
+B<PREV(vname)>
+
+Pushes an I<unknown> value if this is the first value of a data
+set or otherwise the result of vname variable at the previous time
+step. This allows you to do calculations across the data. This
+function cannot be used in B<VDEF> instructions.
+
+B<COUNT>
+
+Pushes the number 1 if this is the first value of the data set, the
+number 2 if it is the second, and so on. This special value, allows
+you to make calculations based on the position of the value within
+the data set. This function cannot be used in B<VDEF> instructions.
+
Z<>
=item Time
=item MAXIMUM, MINIMUM, AVERAGE
Return the corresponding value, MAXIMUM and MINIMUM also return
-the first occurance of that value in the time component.
+the first occurrence of that value in the time component.
Example: C<VDEF:avg=mydata,AVERAGE>
Return the last,first value including its time. The time for
FIRST is actually the start of the corresponding interval, where
-LASTs time component returns the end of the corresponding interval.
+the LAST time component returns the end of the corresponding interval.
Example: C<VDEF:first=mydata,FIRST>
=item TOTAL
-Returns the rate from each defined timeslot multiplied with the
+Returns the rate from each defined time slot multiplied with the
step size. This can for instance return total bytes transfered
when you have logged bytes per second. The time component returns
the amount of seconds