Here are two fascinating barometers. In the top left corner is the smallest, at 34mm overall diameter. It's a late victorian pocket or purse barometer and retailed by Braham Bros of Bath in Somerset. Displaying a range from 25" to 31", the weather predictions 'Rain', 'Change' & 'Fair' as well as an altitude scale from zero to 8000 feet, all engraved on the tiny 30mm diameter dial.
At the other end of the scale is this behemoth barometer at a massive 600mm overall diameter. This instrument has a traditional ropetwist oak frame with a brass bezel on a huge scale and has been completely re-modelled with a period replacement Short & Mason dial and using a  sturdy aneroid movement. Some final cosmetic work could be carried out if required (and doesn't detract) but otherwise ready to hang on a very large wall, (preferably structural!), as it weighs in around 12 Kg.
 
The pocket barometer is for sale at £235
The very large barometer is for sale at £1650