Monitoring grounded ship

The Costa Concordia, which crashed Friday killing six and injuring at least 42, moved 3.5 inches vertically and 0.6 inches horizontally from where it was stranded, due to rough seas, prompting search teams and divers to be evacuated Monday morning, Sky Italia TG24 reported.

Read more: http://www.foxnews.com/world/2012/01/15/third-person-found-alive-after-search-for-survivors-deadly-shipwreck-resumes/#ixzz1jdgW0Wyu

Detected 0.05 feet horizontal movement? I'm impressed. Wonder what they are using to monitor movement.