Barometer World is the world's foremost seller and repairer of antique and modern mechanisms for determining atmospheric air pressure.

A showroom-cum-museum attached to the store features examples of such arcane and wonderful instruments as the "Tempest Prognosticator." Also known as the “Leech Barometer” or the “Atmospheric Electromagnetic Telegraph,” the prognosticator was a 19th-century weather forecasting device that was first exhibited at the Great Exhibition in London in 1851.

A contemporary account of the invention described it as an "elaborate and highly ornate apparatus... evolved by a certain Dr. Merryweather (no epigram intended) who had observed that during the period before the onset of a severe storm, fresh water leaches tended to become particularly agitated. The learned Doctor decided to harness the physical energy of these surprisingly hysterical aquatic bloodsuckers to operate an early warning system. On the circular base of his apparatus he installed glass jars, in each of which a leech was imprisoned and attached to a fine chain that led up to a miniature belfry--from whence the tinkling tocsin would be sounded on the approach of a tempest."

The more bells that rang, the greater the likelihood of an impending storm. A full-scale working model resides in the Barometer World Museum. Another can be found in the Whitby Museum in North Yorkshire.