Kahve Gurtunca 3.0, a Solar Position Module

Software components declare their limits. A validity window, an accuracy figure, a truncation bound: these are stated in documentation and taken on trust by everyone downstream. A declared limit and a measured limit are different objects, and only the second one can be planned against. This paper characterises one solar position module, Kahve Gurtunca 3.0, by measuring what it declares. Three measurement rounds contributed: an initial programme, and two blind re-measurements that received the protocol and none of the results. The headline outcome is not a number, it is a pattern. Accuracy quantities reproduced across rounds to four significant figures in the deviation and to within a tenth of a percent in the sensitivity. A speed quantity did not reproduce at all, differing by a third between two rounds, with neither round wrong. That difference is invisible to a single round, and it is the reason for running more than one. One measured result is reported here because it is the one a reader is most likely to want. Against the reference-grade peer of this field, NREL SPA, on 24,060 points, the two sit 0.09 percent apart in distance to the reference authority, JPL Horizons, and the module's algorithm costs 58 percent of the peer's default path when both are written in one language and timed on one machine. Both halves of that sentence need their qualifications and all of them are given in section 3.5: the measurement cannot separate the authority's own error from either implementation's, so being indistinguishable is not the same as being equal; the cost figure compares algorithms and not shipped artefacts, because the row measured for this module is a translation of it into the table's language; the peer can be compiled instead of interpreted, and when it is, the share rises to 73 percent on one thread and inverts to the peer's favour on its own default of four threads; and the module declares a validity window of two centuries where the peer declares eight millennia, which is where part of the speed is bought. The paper also reports what could not be measured, and why, in the same body text as what could.