+
+=head2 Filtering data
+
+You may do some complex data filtering:
+
+ MEDIAN FILTER: filters shot noise
+
+ DEF:var=database.rrd:traffic:AVERAGE
+ CDEF:prev1=PREV(var)
+ CDEF:prev2=PREV(prev1)
+ CDEF:prev3=PREV(prev2)
+ CDEF:median=prev1,prev2,prev3,+,+,3,/
+ LINE3:median#000077:filtered
+ LINE1:prev2#007700:'raw data'
+
+
+ DERIVATE:
+
+ DEF:var=database.rrd:traffic:AVERAGE
+ CDEF:prev1=PREV(var)
+ CDEF:time=var,POP,TIME
+ CDEF:prevtime=PREV(time)
+ CDEF:derivate=var,prev1,-,time,prevtime,-,/
+ LINE3:derivate#000077:derivate
+ LINE1:var#007700:'raw data'
+
+