A fitted case with an empty recess invites a guess about what belonged there. A documented packing diagram can provide stronger evidence than matching the recess to the first familiar shape that comes to mind.
Start by identifying the exact set or model represented in the diagram. Similar cases can hold different combinations, so a family resemblance is not enough to establish the contents.
Match position and identifier together
In a practice note, assign each visible recess a temporary letter. Beside it, record the corresponding item number from the diagram, or mark the relationship as uncertain. Keep your temporary letters distinct from historical numbering.
An invented example might contain six compartments but only five listed tools because one compartment holds a supply packet. Counting spaces as tools would create a false missing item.
Do not insert objects into a historic case to see what fits. Shape comparison can remain visual, using the institution’s measurements and photographs.
Your conclusion should distinguish “the diagram lists this component” from “this particular set originally contained it.” Provenance or acquisition records may be needed for the second claim. A careful map narrows the question without pretending that an empty space tells its whole history.
Editorial illustration from this site’s image library; not documentary evidence of the example or object discussed.