Did you know that an inch is defined to be 2.54 cm ? Then the mile is exactly 5280 X 12 X 2.54 cm = 1609344 mm, exactly. So hey! How metric can you get?
Millibars are the familiar unit for people in weather forecasting. Weather maps have been issued in 4 or 5 mb contours for at least half a century and probably longer. People in the weather business talk to each other in millibars and not inches or mm of mercury. If you were in any given weather office, private or government, you would hear people talking about for example a 965 low meaning it had a central pressure of 965 millibars.
All you really need to know about millibars is that 1013 is the global average and anything over 1040 is quite high, anything under 960 is quite low. I do have a home barometer that measures in inches so I’m used to making conversions in my head. This has probably been stated earlier in this thread, but 1000 millibars equals 29.53 inches and so 1050 millibars, about the highest pressure most people see in an average winter, would be 5% higher. That would add 5 x .295 inches or 1.48 inches rounded off, so in other words 31.01 inches and I think you’ll find that your home barometer shows this as being fairly high. A very deep low at 950 mbs would then be an equal amount lower, or 28.05 inches.
Sometimes in metric countries you will hear pressure given as kilopascals, these are scaled like millibars but ten times smaller so that 1000 millibars would be 100 kilopascals. So if you ever hear that type of pressure reading just multiply it by 10 to convert to millibars.
That typhoon last November in the Phillipines reached a minimum pressure of about 890 millibars. You can see why weather people prefer it, the relativity aspect is very obvious since the mean is more or less 1000 millibars.