In the sequential approach, a single species is added by referencing it to species already in the thermochemical network. These species can be the elements in their standard states (anchors) or species that are connected to the elements, i.e. their ∆ f H is known (references). The expansion of the thermochemical network is most commonly done one species at a time, which introduces a few issues. Foremost, it requires the constructor of the sequential compilation to choose at the onset which species to add and in which order. Imagine that there are two species with similar quality thermochemical determinations (e.g. two different reaction enthalpies forming the target from references) that relate both to the existing compilation. The constructor of a sequential compilation must arbitrarily choose which to add first, artificially diminishing the impact that the second has on all subsequent determinations. Once a species is added, values for its enthalpy and partition function are adopted, and all additional species that include a reference to that species, even indirectly, depend explicitly upon the previous values. The choice of partition function determines how a species thermochemical information is converted to the reference temperature of 298.15 K under standard conditions at which the thermochemical network is solved. Thus, partition functions can limit the accuracy as many determinations occur at temperatures far from the reference temperature. The third issue is bias because constructors have to weigh all the available information when choosing what values to recommend for a given reaction enthalpy. Frequently, the constructors adopts a single "best" determination to add a new species to the network, discarding the remaining information. Importantly, new information that becomes available after a value has been adopted cannot be included without redoing the entire compilation of the network, which is the largest problem with the sequential compilation. By the time a sequential network is compiled there is likely better or contradictory information that cannot be included without introducing inconsistencies. Examples of these sequential thermochemical networks are the JANAF tables or the NIST Chemistry WebBook .