As new altitudes are issued, all of the strips for that aircraft must be annotated with the new data and separation checked again at all of the intersections it passes through. This is more laborious than the altitude method of grouping where only one strip is needed, but possible conflicts between multiple aircraft climbing and descending are easier to discern or discard this way since all intersection points and times are pre-calculated and laid out separately. With the altitude grouping method, if two aircraft are determined to conflict based on altitude, the controller must then manually determine the intersection points and times to further determine or rule out the conflict.