The equivalents of Ottoman weights and measures in pre-metric and metric systems: the early comparisons and conversion tables
The attempts to transfer and adopt the European science and technology unavoidably brought along the need to compare the Ottoman measures with their European counterparts at the end of the eighteenth century. The Mühendishane ( Engineering School ) that was a forerunner in the introduction of European techniques into the Ottoman Empire played a similar role in the field of metrology. Political conditions of the late eighteenth century led to the recruitment of French and English experts in the Mühendishane, whereas the employment of texts translated from these languages for engineering education rendered it necessary to ascertain the Ottoman equivalents of French and English measures. Thus, a comparison was made between the French kadem and the Ottoman zira and the results were published by Hüseyin Rıfkı Tamanî in his Telhis-ül Eşkal (written in 1794, printed in 1801) and Mecmuat-ül Mühendisin ( Istanbul , 1805). Once the ratio between the French and Ottoman measures was known, it became much easier to calculate the Ottoman equivalents for the measures of various countries since the equivalence of French measures with the others was already known.
Starting from the first half of the nineteenth century, metric weights and measures became included in the European books of science and technology. Ottoman engineers mentioned metre in the books they translated or compiled from Europeans sources and calculated the metric equivalents of Ottoman weights and measures. In the calculation they used the results of the comparisons made by H. Rıfkı between the Ottoman measures and the pre-metric French measures (6 usbu-i osmani=7 usbu-l françe).
The direct comparison of the zira to the metre was made in 1841 in Paris through the initiatives of Mehmed Emin Pasha, which was an important step in the standardization of Ottoman measures of length. The value of 0,757 738 m. was accepted as the official metric equivalent of the zira after the adoption of the new system by the Ottoman government in 1869. The metric equivalent of okka (1,282 945 kg.) as calculated by Mehmed Emin Pasha in 1842 was officially included in the conversion tables. These values rounded as 0,758 metres and 1,283 kilograms were frequently used in the conversion tables from 1870s on. On the other hand, the metric equivalent of zira (0,757 9586 m.) calculated by İshak Effendi (1834) and İbrahim Pasha (1836) based on the measurements made in Istanbul at the end of the eighteenth century by Tamanî approximated the value obtained in Paris in 1841 by using a comparator equipped with microscopes.