No problem,
My Suggestion is to have a relationship where One Inventory has Many Check In / Checkouts.
The Check In Check our record will have a status as to if its is checked In or and obviously who has the inventory item now if it's checked out.
So the trick is how you get that information of the most recent Check In Check Out record floated up to the Parent.
Go to the Relationship and make a Summary field of the Maximum Record ID, and call it [Record ID# of the Most Recent Check In / out]
Then make a new "reverse relationship" where One Check In has Many Inventory items. Yes, that does sound backwards and that is why it is called a Reverse Relationship.
On the right side of the relationship, do not let Quick Base create a new field, instead use the field you just created [Record ID# of the Most Recent Check In / out] and do not select an lookups until you save the relationship.
Then edit the relationship and lookup the status (check in or checked out) and who has the Inventory item.
Now those fields are on your parent Inventory Item Y're done!
If you still have that ACTION, get rid of it as this method does not need an ACTION and is more transparent to users.
