Salas E., C., M. Reyes Sch., and C. Bassaber E. “Measurement of Upper-Stem Diameters With Bitterlich Mirror Relascope and Finnish Parabolic Caliper: Effects in Volume Estimations”. Revista Bosque, vol. 26, no. 2, Aug. 2005, pp. 81-90, https://revistabosque.org/index.php/bosque/article/view/1008.