Some of the most widely utilized measurements in plant science research, such as total protein content or chlorophyll (chl) determination, are both straightforward and indispensable. The accuracy of the techniques employed for the quantification of these compounds is an important part of laboratory work, which will compromise the further determinations and even the conclusions of many of the articles published now and in the future. For the topic of this Letter, chl determination, a complete set of methodologies, from remote sensing to chromatographic analyses, are available (Blackburn & Ferwerda, 2008; Cortazar et al., 2015; Junker & Ensminger, 2016). Among this broad array of methodologies, one of the most (if not the most) successful protocol for the simultaneous quantification of chla and b is the one described by Arnon in the middle of last century (Arnon, 1949). Evidence of its success is the fact that it has received almost 14 000 citations up to now and it has been in the top 100 most cited papers of all time (Garfield, 1990) for decades, a position only recently lost (it ranks 139th, July 2017). Even so, Arnon's paper is frequently cited even now (actually, it is one of the four most‐cited papers ever in the area of Plant Science, according to the Web of Sciences, 2017). In fact, the highest number of citations was recorded in 2014, 2015 and 2016 (Fig. 1). Interestingly, chl determination was not the main achievement of this paper, which focused on copper metabolism in chloroplasts. However, the equations proposed for chl measurement became the reason for its success. In fact, his previous Nature paper on copper (Arnon, 1948) has only received 15 citations since its publication. Despite their great success in numeric terms and in spite of the fact that they enjoy such a huge following, Arnon's equations are based on old and inaccurate molar extinction coefficients calculated for 80% acetone as solvent.