The package can be compressed using a plate (wood or steel) and well defined loads. You can get a well-defined load but it is difficult to measure the compression distance. The problem is that the plate is floating and you cannot be sure that the plate and the floor are parallel. The floating situation results also in lower performance than a compression tester because you are only measuring the weakest spots on the package. Different distribution of loads onr the plate will result in different test results.