Answer:
mm Hg
Explanation:
In those early barometers the concept to measure the pressure was to find the displacement of the mercury in the barometer tube
So here in that barometer when mercury filled tube is inverted into the mercury filled container then the level of mercury is at some height
When we measure that height then it will help to find the pressure
\(P = \rho g h\)
since we used mercury in this experiment
so the length of the mercury in this tube is given as pressure units
so one of the unit is known as
mm Hg
