There's vertical spacing of 1/24″ in some places, which is twice the usual Selectric precision (6lpi with half-line motion). To me the most likely explanation i

There's vertical spacing of 1/24″ in some places, which is twice the usual Selectric precision (6lpi with half-line motion). To me the most likely explanation is a Selectric variation with twice the detents, or even a third-party add-on, made specifically for technical reports.