Enter a formula in this field. Valid variables are (open the Variables menu):
U, V, W: The UVW coordinates
X, Y, Z: The spatial coordinates
t: Time in seconds
User Data: User Data that you define (in the following example: Factor)
As always, the formulas in the Attachment are valid for all numeric fields; for users with more pronounced math skills, these can be used to create a wide range of effects.
If you use position coordinates within the formula you can switch between the local (option disabled and the coordinate system of the object to which the material is assigned will be used) and global coordinate systems.