  Stellar elemental abundances are important for understanding the fundamental
properties of a star or stellar group, such as age and evolutionary history, as
well as the composition of an orbiting planet. However, as abundance
measurement techniques have progressed, there has been little standardization
between individual methods and their comparisons. As a result, different
stellar abundance procedures determine measurements that vary beyond quoted
error for the same elements within the same stars (Hinkel et al. 2014). The
purpose of this paper is to better understand the systematic variations between
methods and offer recommendations for producing more accurate results in the
future. We have invited a number of participants from around the world
(Australia, Portugal, Sweden, Switzerland, and USA) to calculate ten element
abundances (C, O, Na, Mg, Al, Si, Fe, Ni, Ba, and Eu) using the same stellar
spectra for four stars (HD361, HD10700, HD121504, HD202206). Each group
produced measurements for each of the stars using: 1) their own autonomous
techniques, 2) standardized stellar parameters, 3) standardized line list, and
4) both standardized parameters and line list. We present the resulting stellar
parameters, absolute abundances, and a metric of data similarity that
quantifies homogeneity of the data. We conclude that standardization of some
kind, particularly stellar parameters, improves the consistency between
methods. However, because results did not converge as more free parameters were
standardized, it is clear there are inherent issues within the techniques that
need to be reconciled. Therefore, we encourage more conversation and
transparency within the community such that stellar abundance determinations
can be reproducible as well as accurate and precise.
