It serves as a hypothesis that explains our observation. There are many reasons for this observation in nature. Plato expressed hostility to observation and experiment. There is never passive observation or knowledge. Thus redshift is a quantity unambiguous for experimental observation. Popper rejected the way that empiricism describes the connection between theory and observation. It tends to be less precise than sensors based on stellar observation. In measurement the number of standard units which is equal to the observation is counted. The latter case was exemplified by astrology, which appeals to observation and experimentation. Examinations combine the hierarchical observation with judgement. Diagnosis is by symptom observation and investigation of the person's history. LDA works when the measurements made on independent variables for each observation are continuous quantities. An OBR Segment carries information about an exam, diagnostic study/observation. Cook's distance measures the effect of deleting a given observation. Navigation relies heavily on constant observation and memorization.