Historical star magnitudes from catalogues by Ptolemy (137 AD), as-Sufi (964) and Tycho Brahe (1602/27) are converted to the Johnson V-mag scale and compared to modern day values from the HIPPARCOS catalogue. The deviations (or "errors") are tested for dependencies on three different observational influences. The relation between historical and modern magnitudes is found to be linear in all three catalogues as it had previously been shown for the Almagest data by Hearnshaw (1999). A slight dependency on the colour index (B-V) is shown throughout the data sets and as-Sufi's as well as Brahe's data also give fainter values for stars of lower culmination height (indicating extinction). In all three catalogues, a star's estimated magnitude is influenced by the brightness of its immediate surroundings. After correction for the three effects, the remaining variance within the magnitude errors can be considered as approximate accuracy of the pre-telescopic magnitude estimates. The final converted and corrected magnitudes are available via the Vizier catalogue access tool (Ochsenbein, Bauer, & Marcout, 2000).

中文翻译：

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望远镜前星表中的星等精度

来自托勒密 (137 AD)、as-Sufi (964) 和第谷布拉赫 (1602/27) 星表的历史星等被转换为约翰逊 V 级星等，并与来自 HIPPARCOS 星表的现代值进行比较。测试偏差（或“错误”）对三种不同观察影响的依赖性。历史和现代量级之间的关系在所有三个目录中都被发现是线性的，正如 Hearnshaw (1999) 先前对 Almagest 数据所显示的那样。整个数据集都显示了对颜色指数 (BV) 的轻微依赖，as-Sufi 和 Brahe 的数据也给出了具有较低顶点高度（表明灭绝）的恒星的较暗值。在所有三个目录中，恒星的估计星等都受到其周围环境亮度的影响。在对三种效应进行校正后，震级误差内的剩余方差可以被认为是望远镜前震级估计的近似精度。通过 Vizier 目录访问工具 (Ochsenbein, Bauer, & Marcout, 2000) 可以获得最终转换和校正的震级。