Variogram forms
In most forms, the solver fills in one letter per space. In a variogram form—most often a square—a space might contain just one letter, or might contain any number of letters more than that. See the example in the square description.
Variogram forms are often significantly harder than standard forms. Generally, it is best to clue them as straightforwardly as possible.
Formists often compose variogram squares to incorporate some specific idea; for example, to include the sequence NPL in a number of places, or to have a pattern in the number of letters used in each space.
In a space where a word crosses itself—such as the first space in a square—having a long multi-letter sequence can be problematic for solvers. Multi-letter sequences should generally be included in two words.