Anemometer Lind was not the first it was the most practical and best known anemometer of this type. If the wind blows into the mouth of a tube it causes an increase of pressure on one side of the manometer. The wind over the open end of a vertical tube causes little change in pressure on the other side of the manometer. The resulting elevation difference in the two legs of the U tube is an indication of the wind speed. However, an accurate measurement requires that the wind speed be directly into the open end of the tube; small departures
Gibbs measure property. Measures with this property are sometimes called Markov random fields. More strongly, the converse is also true: "any" positive probability distribution (nonzero density everywhere) having the Markov property can be represented as a Gibbs measure for an appropriate energy function. This is the Hammersley–Clifford theorem. What follows is a formal definition for the special case of a random field on a lattice. The idea of a Gibbs measure is, however, much more general than this. The definition of a Gibbs random field on a lattice requires some terminology: We interpret as the contribution to the total energy (the Hamiltonian)