TECHNICAL OR SCIENTIFIC DEFINITION OF NEGATIVE FOR COVID . The PCR or PolymerASE Chain Reaction is a test in which a DNA fragment is duplicated such a number of times that it is made very easy to detect the presence of viruses, bacteria and other pathogens, MOLECULAR MEDICINE, as well as determine murder-causing, paternity and many crimes. The duplication is done every hour approximately and at 30 hours we have about 1.2 billion duplications which makes the analysis very accurate. The result, when we are looking for SARS covid-1can give positive (sick) or negative (healthy) , that is, it gave negative for SARS covid-19, but it is not pronounced over other pathogens. Now, some erroneous results are given, false positives and false negatives. They shrink as duplication increases. 1000 million is a large enough number, but it is not 100% accurate. For this reason the results take from 2 to 3 days (and more in pandemic, due to the at nighting of samples)