I have inherited a barometer than only has units of inches. I was wondering what that meant and how to link it to the Internet readings in millibars. Then I found this one that has both scales. I think that inches refers to a mercury barometer, where the air pressure supports a column of mercury. These days, the units are usually given as mmHg. Now I can see that 1000millibars would support a column of mercury that just over 29.5 inches high.
