Mintrop (built sometime after 1910)
From the very large (last week's 19-ton seismograph) to the relatively small : the Mintrop portable horizontal seismograph.
The Mintrop is an odd instrument, that measures horizontal motion using a damped inverted pendulum with a horizontal rotation axis. Its relatively small mass is coupled with a vertically oscillating mirror and an optical recording system.
Given the delicate nature of the recording system, the Mintrop must have been rather difficult to install. It is considered to be one of the first portable field instruments, and was used for early prospection studies by German oil companies.