This discussion includes: • Correctness of an assumption, • Implied lack of rigor in cited work, and • Challenge to authors’ claim to first publication. Soler and Smith use two rotation matrices in their derivation— one at the standpoint (point 1) and the other at the forepoint (point 2). That creates two problems: 1. Computing local components of geocentric coordinate errors at points 1 and 2 using Eqs. (1) and (2) in Soler and Smith’s paper represents legitimate mathematical operations, but local east/ north/up (e;n;u) values at point 1 are not compatible with local e;n;u values at point 2 because separate rotation matrices were used, making the orientation of the two axes different. Therefore, local error differences as computed by the authors’ Eqs. (6a), (6b), and (6c) do not reflect the local error in the position of point 2 with respect to point 1. 2. The use of two separate matrices by Soler and Smith is also reflected in their Eq. (10), where separate rotation matrices are used at points 1 and 2. That flaw is propagated into their Eq. (14), which does not give a correct expression for the local accuracy of point 2 with respect to point 1. In short, the rotation matrix of point 2 [R2] should not be a part of their derivation. But Soler and Smith’s extension of Burkholder’s previous work can be salvaged if one uses the rotation matrix at point 1 to compute local e;n;u errors at both points 1 and 2. With that modification, the local error differences found in their Eqs. (6a), (6b), and (6c) will correctly represent the positional error of point 2 with respect to point 1. The defect in Soler and Smith’s Eq. (14) is remedied by replacing the rotation matrix at point 2 [R2] with the rotation matrix at point 1 [R1]. The appendix of this discussion contains an alternate derivation of Soler and Smith’s Eq. (14) based upon the fundamental errorpropagation equation, the covariance matrix of the vector from point 1 to point 2, and the partial derivatives of point 2 with respect to point 1. The following points are also made: • Soler and Smith acknowledge that treatment of local accuracy as given in Burkholder (2008) may be assumed to be conceptually correct. This discussion shows that Burkholder’s treatment is also fully rigorous. • A mathematical definition of local accuracy was published in Burkholder (1999) and cited in Burkholder (2008). • The concept of local accuracy is described in Burkholder (2008). The local accuracy concept is identified in Chapter 1 as part of the stochastic model, is included in Chapter 11 in the GPS network example, and is demonstrated by a spreadsheet example in Appendix C. Related Comments