There are 2 slots of varying thickness (go/no go) in which the product must pass or not pass through. If the product is too thin and goes through the "no go" side, it is rejected. If the product is too thick and won't go through the "go" side, it is rejected. Our assumption was that the maximum degree of unflatness that a part could demonstrate would be the difference between the measurements of each slot.
Perhaps you could check its function by using not a toaster but two flat planes (covering the entire surface if that is the equivalent to how it is used), separated by gauge blocks? I used to do this to check that gears to a pump would be neither too thick or distorted by heat treatment (would have caused them to seize up) nor too thin (not enough pump pressure due to oil escaping through the gap).
However, the customer is applying pressure to one side of the filter and measuring the length the other side rises off of a flat surface. I tried to argue that this is magnifying the degree to which the product is not flat but they insist their method is correct.
This is getting interesting. Please let us know how it ends.
/Claes