Another method of analysis measures the peaks in relation to one another. In this method, the tallest peak is set at 100%. The other peaks given a value equal to the ratio of the peak height to the tallest peak height. All values above 3% are assigned. The total mass of the unknown compound is normally indicated by the parent peak. The value of this parent peak can be used to fit with a chemical formula containing the various elements which are believed to be in the compound. The isotope pattern in the spectrum is unique for elements that have many isotopes. So, it can also be used to identify the various elements present. This tells the overall chemical formula of the unknown molecule. Because a molecule's structure and bonds break apart in characteristic ways, they can be identified from the difference in peak masses. The identified molecule structure must be consistent with the characteristics recorded by GC-MS. Typically, this identification is done automatically by computer programs which come with the instrument. Those programs match the spectra against a library of known compounds that have same list of elements which could be present in the sample.