PSP is a form of atypical parkinsonism. That is, the symptoms of PSP disease may in part resemble normal Parkinson's disease, for example, because of the slowness and rigidity that are common to both conditions. Yet the underlying disease process is substantially different. People with PSP are often mistakenly thought to have Parkinson's disease at first. It is therefore important that a new, more reliable measuring instrument is developed for this atypical parkinsonism.