Consists of the records (1760-1974) of a large business conglomerate in northern Mexico founded by Pedro R. Prieto and owned by branches of the Prieto family, including Maíz family members, for three generations.

The first report presents a chart method for calculating the characteristics of a reactor. The second report offers a set of universal curves which could be used to find the characteristics more easily. The third report describes in more detail two specific uses of the universal curves which were not covered in the second report, namely calculation of the d-c flux linkages in the reactor and calculations of problems involving rectifiers.