Best way to check if ICP produces good transformation

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Hi

I have a lidar that is poorly calibrated in the factory and this lidar can produce two point clouds that are not well aligned if lidar scans the same object and both lidar and object are fixed. I calibrated two misaligned point clouds using the ICP algorithm in PCL. How can I check if the final transformation from the ICP algorithm is good enough? My idea is that we need to measure the distance between the final transformation and the identity matrix. That is the euclidean distance between two matrix or frobenius distance. Any better idea?