How to Adjust a Barometer

Barometers are essential to accurate weather forecasting. As with any precision instrument, barometers must be routinely calibrated to accurately capture atmospheric data.

Quick Adjustments
To guard against misleading displays of information, calibrate every new barometer with these following steps:

Current Reading: First, get the current barometric reading for your area. Local weather reports are a good source. The internet is also a valuable resource for finding accurate barometer readings.
Look in Back: Behind the barometer is a small hole with a small screw set deep inside. Get at that screw with a very small screwdriver.
Adjust the Hands: Watch the dial on the front of the barometer. Make sure the indication hands are moving clockwise. Set to the current barometer reading for your area.

It's All Relative
Keep in mind that barometers have no absolute value. "Sea Level" is the standard setting, but that just makes world-wide measuring and comparison easier. What a barometer displays is relative change. For that purpose, barometers have a knob on front to move an indicator. Set it to your current barometer reading. Using this larger hand as a starting point, the barometer is ready to gauge change and help forecast weather.

Frequent Calibration
Occasionally check the barometer reading against the current broadcast reading from weather sources. Over time, the springs in the barometer mechanism get loose. Tuning the device is simply a matter of retightening screws.

Reading the Data
The most important part of any instrument is interpreting data. Even basic barometers, when read properly, can reasonably predict weather for the next 24 hours (as long as you know how the data has changed). In general, a change on the barometer means something's going to happen in the sky.