Ebbco began making inexpensive plastic sextants for emergency or educational in the 1960s. In this example, the arc is graduated every degree from -10o to 120o and read by micrometer with vernier to 12 seconds of arc. Ref: J. P. G. Weatherlake, The Ebbco Sextant. Its Use, Care and Adjustment (n.p., n.d.).
