01
Separate shared items from window-only items
The shared IDs are P, Q and S, giving three shared items out of five in each window. The overlap share for either supplied list is therefore three fifths, or sixty percent. R and T appear only in A; U and V appear only in B. Across the two lists there are seven distinct IDs. If using intersection divided by union instead, the value is three sevenths, about forty-three percent. Name the denominator whenever reporting a percentage because these two calculations answer different questions about the same pair of lists.
02
Describe position changes only for shared IDs
P moves from position one in A to position two in B, while Q moves from two to one. S remains at position four. R and T have no supplied position in B; their absence from this five-item window does not establish where they appear elsewhere. Similarly, U and V have no supplied position in A. Keep those positions blank with an explanatory status rather than assigning zero. A zero would introduce a position that the example never observed and could distort a later calculation of movement.
03
Save the conditions needed for a useful comparison
A reusable comparison record includes the exact query, source or catalogue, capture references, timestamps, window size, item identifiers and ordered lists. Add viewing conditions when known and label missing conditions explicitly. Before attributing differences to an update, establish which conditions were held steady and what independent evidence supports that explanation. The worksheet can report the visible changes immediately while leaving their cause unresolved. If a later capture expands the window, retain the original five-item observation and create a separate comparison with the new boundary.