Figure 1 : This is the standard equipment for TLC / HPTLC quantitation andsubstance identification by UV and VIS spectroscopy. However no correct plate structure correction. By single scans of linear tracks is only one correction mathematically correct: the systematic signal error caused by plate structure cannot be treated like electronic noise but only by subtraction. There is however also real noise caused by the scanner electronics which is reduced by signal smoothing. The signal errors caused by plate vibration - which is possible and depending from the plate weight, plate position and scan conditions is a next problem. All these false signals are responsible for a relatively bad data quality. This critical statement is based on the data quality existing in gas- and column liquid chromatography.