Informal currencies such as Local Exchange Trading Systems (LETS). LETS involve the creation of notes or equivalents such as Ithaca Hours that represent a specified quantity of labour time. With Ithaca Hours a unit is valued at $10, and while most work is valued as one unit, certain professionals like dentists are allowed to value their hour more highly. Most schemes are limited in size (Ithaca Hours was one of the largest with 1400 members at one time). In the UK where there are some 300 LETS schemes, the average size is 100 members. They are used for person to person exchanges and loans, as well as for partial payments in the market economy.