Contrary to many advanced applications of the two-dimensional correlation spectroscopy that have been presented at the 2DCOS-3 conference we have focused on some basic aspects concerning visualization of the 2D results. After introducing the generalized 2D correlation, when the simple analytical expression replaced the complex Fourier transforms, the number of new users has been substantially increasing. In many cases it was revealed that analysis of a studied system could be essentially improved whenever the 2DCOS method is applied. A lot of useful information is available from the 2D spectra when analyzed according to the guidelines that are popularly known as Noda's rule. One of the most important information provided is the sequence order of events observed by the spectroscopic technique along the external perturbation. It finds excellent application in many studies, e.g., the investigation of the evolution of the unfolding mechanism of proteins. For such complicated systems most 2D features can be interpreted in a frame of the unfolding process. However, this information is not easily verified by other techniques. Therefore, we have to be very careful that this stage of 2D correlation is performed and interpreted correctly.

We will present a problem that is often overlooked in the visualization of the 2D data and that can lead to a misinterpretation of results, concerning orientation and labeling of the axes of 2D contour plots. In certain cases the orientation of 2D plots may be altered and obtained peaks could have a false sign, resulting in incorrect interpretation. On simulated data we will demonstrate these potential pitfalls that lurk for new 2D users and can finally lead to an inversion of sequence order of events. (c) 2006 Elsevier B.V. All rights reserved.