A look at the internals of the Brunsviga Model A and Marchant EEG9 mechanical calculators, as well as a brief description of how pinwheel calculators work.

Brunsviga Model A - introduced in 1894
Marchant EEG9 - introduced in 1927 (one of the most advanced pinwheel calculators ever made - after this Marchant switched to their silent speed proportional gear calculators. Other companies such as Hamann Manus made pinwheel calculators of similar complexity)

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