fractional index or x
The index or x-value at which the node should return a y-value.fractional index or x must be located directly on a point or between two points for the node to work correctly.
fractional index or x does not interpolate beyond the bounds of an array or data point set. For example, if the parameter is set lower than the first element or x-value in an array, the node returns the value of the first element or the y-value of the first data point. Similarly, if the parameter is set too high, the node returns the value in the final element or the final y-value.