Weather Monitoring Instruments A range of quality weather instruments with brass bezels and glass covers. (56.6mm approx hole size required) How to set up you Barometer Listen to a local weather forecast to find the current barometer pressure for your location. ... Set the black indicating hand. ... Adjust the set hand, or pointer. ... Use your barometer to forecast the weather. ... Check occasionally to be sure that your barometer works properly or whenever you suspect inaccurate readings.