+Round down or up to the nearest integer.
+
+B<DEG2RAD, RAD2DEG>
+
+Convert angle in degrees to radians, or radians to degrees.
+
+B<ABS>
+
+Take the absolute value.
+
+=item Set Operations
+
+B<SORT, REV>
+
+Pop one element from the stack. This is the I<count> of items to be sorted
+(or reversed). The top I<count> of the remaining elements are then sorted
+(or reversed) in place on the stack.
+
+Example: C<CDEF:x=v1,v2,v3,v4,v5,v6,6,SORT,POP,5,REV,POP,+,+,+,4,/> will
+compute the average of the values v1 to v6 after removing the smallest and
+largest.
+
+B<AVG>
+
+Pop one element (I<count>) from the stack. Now pop I<count> elements and build the
+average, ignoring all UNKNOWN values in the process.
+
+Example: C<CDEF:x=a,b,c,d,4,AVG>
+
+B<TREND, TRENDNAN>
+
+Create a "sliding window" average of another data series.
+
+Usage:
+CDEF:smoothed=x,1800,TREND
+
+This will create a half-hour (1800 second) sliding window average of x. The
+average is essentially computed as shown here:
+
+ +---!---!---!---!---!---!---!---!--->
+ now
+ delay t0
+ <--------------->
+ delay t1
+ <--------------->
+ delay t2
+ <--------------->
+
+
+ Value at sample (t0) will be the average between (t0-delay) and (t0)
+ Value at sample (t1) will be the average between (t1-delay) and (t1)
+ Value at sample (t2) will be the average between (t2-delay) and (t2)
+
+TRENDNAN is - in contrast to TREND - NAN-safe. If you use TREND and one
+source value is NAN the complete sliding window is affected. The TRENDNAN
+operation ignores all NAN-values in a sliding window and computes the
+average of the remaining values.