Vidal, A., Orozco, L., Arregui, S., Sánchez, J., Gálvez, O., Méndez, I., & Inzunza, L. (2003). A note on upgrading long-period seismographs. Geofísica Internacional, 42(1), 53–59. https://doi.org/10.22201/igeof.00167169p.2003.42.1.359