I am about to embark to a trip in which the Control/Approach Center gives pressure in millibars(MB). By writing this small tutorial I would commit to memory a simple formula that will help me convert millibars to inches of mercury. My aircraft does not have the capability of dialing the MB so this formula will come in handy.
Whatever MB Center gives you, multiply it by 30″ and dived it by 1016MB. the result would be the pressure to input in your Kollsman window.
It so happens that MB is a linear function to inch of MG. at 1016 MB is 30 inches of Mercury therefore a simple proportion converts from one units to the other. eg 980 MB is 980*(30/1016)=28.937 (28.94 on Kollsman Window)
Hope this comes in handy for you also and maybe if a question pops up in one of your FAA written test you could ace the question.