The Metric system was optional from 1857, and has been compulsory since 1896.
[1][2] The Units of the system (from Spanish, Castillian) were legally defined during the transition period of the metric system.
[1] Some other units and legal equivalents are given below: 1 linea (lit.
"thumbful", "inch") = 1⁄36 vara 1 pie (lit.
"pound") was equal to 0.46024634 kg as it was legally defined.