Occassionally it is useful for the user to override the value of a uv variable.
This is especially useful if the value of the variable is both wrong and
important! When uvio opens an old file, for each variable name that is
present in the uv file, it checks if there is a corresponding item with
the same name. If there is, then the value of the item is used to override the
value of the variable. Unfortunately the item must consist of a single
number, and this single number will be copied into each value of the variable
(if the variable consists of several elements).