The value in a particular field may not be free to vary and instead may depend on the value in some other field. One of the ways that such dependence makes itself most apparent is when a weighting field shows only agreement. For example, suppose the investigator chooses to block on the Principal's Given Name Code. The code is derived from the actual spelling of the name. The custom in many countries is to choose a name for an individual according to the sex of the child. For example, "Ann" is a given name for girls and "William" is a given name for boys. Now what happens if we weight on the Principal's Sex? Every record in the block already has the same name code. Since the name was chosen according to the sex of the individual, then weighting on Principal's Sex simply adds a particular additional weight to every record in the block. However, if the same code were given to "Harry" and "Harriet", for example, then weighting on Principal's Sex could be helpful.