Following the pioneering work in the PhD dissertation by Snow (PhD thesis, Rep. No. 502, Div. of Geodetic Sci, School of Earth Sciences, The Ohio State University, Columbus, OH, USA, 2012), the two articles by Schaffrin et al. (J Geodetic Sci 4(1):28–36, 2014) and by Jazaeri et al. (Z für Vermessungswesen 139(4):229–240, 2014) provided a broad overview of the Total Least-Squares (TLS) adjustment within EIV-Models with singular cofactor matrices. Around the same time, Xu et al. (J Geodesy 86:661–675, 2012) proposed a specific algorithm to find the TLS solution within a partial EIV-Model, which has been improved by various authors since, including Shi et al. (J Geodesy 89(1):13–16, 2015), Wang et al. (Cehui Xuebao/Acta Geodaet et Cartograph Sinica 46(8):978–987, 2017), Zhao (Surv Rev 49(356):346–354, 2017), and Han et al. (Surv Rev 52(371):126–133, 2020), to name a few. On the other hand, it is easy to see that the partial EIV-Model is a special case of the general EIV-Model with singular cofactor matrices and thus does not need a separate class of algorithms unless they are more efficient than the standard algorithms. This, however, does not seem to be guaranteed as will be shown in this contribution for the straight-line adjustment under $$Q_A = Q_0 \otimes Q_x$$
Q
A
=
Q
0
⊗
Q
x
. As a consequence, we shall argue that, rather than discussing the partial EIV-Model, it would be more worthwhile to make the respective developments within an EIV-Model with singular cofactor matrices directly.