LB, our instrument shop was using a Hg barometer for calibrating our other instruments right up to my retirement about 20 years ago. All other Hg instruments were gone.
One that we had used was a USGS servo-manometer, in which one arm of a manometer was connected to the back pressure of a gas bubbled to an outlet in the river, while the other arm held a Hg reservoir with a float switch. a change in water level resulted in a rise or fall in the Hg in the other arm. The float switch would activate a servo motor to raise or lower the reservoir to the null position, and also drive a pen across a chart recorder. The constant flow, constant pressure gas regulators had to be adjusted in a particular sequence, and inevitably, there were times when they weren't, resulting in an expensive and dangerous mercury spill.