Pocket barometer is self-explanatory in that it often fits in a pocket, usually that of a Victorian gentleman's waistcoat. It is not until the early 1860s that they were made, using Vidi's patent design. Negretti &Zambra are credited with making a portable barometer in 1864 of 1 ¼" diameter.Most pocket barometers one sees today are approximately 2" in diameter.Many have altimeter scales and gentlemen will have used these to check altitude when travelling to foreign parts.Often they come with finely made morocco covered cases to protect them; some have thermometers within and a few have compasses.Occasionally silver cased models become available and very rarely, gold ones.Larger pocket barometers, perhaps more correctly termed surveying aneroids, are also covered in this category.Some of these will have magnifying lenses to see the finer variations and occasionally verniers to make more accurate readings on the dial.