The offline quality check is as essential as the online checking that the shifter does. The online checking can only check that the detector is working as it should at the moment of the check. If intermittent errors occur they can easily be missed. Fortunately there is also a central shifter on place at DELPHI that checks the VSAT histograms more frequently. It is however only offline you can get a total picture that the data is correct. Bugs in DELANA can also only be spotted offline, which makes it vital to check the offline histograms frequently.
The VSAT shifter can on the other hand not spend his time checking every fill for errors, as he wouldn't be doing much else then. For every 10 fills a user-friendly output should be generated, which the shifter easily could check. The first level output should only contain the most vital information from the detector, which the shifter checks for each fill. If problems or strange distributions are found, there should exist a second level output that could clearify the source of the problem.