Indexed sequential access methods allow finding the keys (having associations) closest to a given value. This facilitates the interpolation of associations between those in the table.
Table should be a relational table with one numeric primary key
field which supports the
operations. column should be a symbol or exact positive integer
designating a numerically valued column of table.
interpolate-from-table calculates and returns a value
proportionally intermediate between its values in the next and
previous key records contained in table. For keys larger than
all the stored keys the value associated with the largest stored key
is used. For keys smaller than all the stored keys the value
associated with the smallest stored key is used.