From the top:

A mechanical calculator. Not sure which type. Looks very much like the Facit Standard

A detail of the triangulation of Hanover carried out under Gauss’s supervision between 1820 and 1850 . The pink lines are part of the Hauptsystem (main system) laid out by Gauss himself in 1821-1825. From his Collected Works, Volume 9, p. 347.

A Chinese orrery. If you zoom in you can see some Chinese constellation names.

Another illustration of Gauss’s survey, from 10 Deutsche Mark, Series 4, backside

A page from Thesaurus logarithmorum completus (1st edition 1794, 90th edition 1924) by Jurij Vega“

A part of the moon, at None

The portrait of Cosmia is by leffenkitty

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