Parameter corresponds to the sampling interval, and this Fourier series can now be recognized as a form of the Poisson summation formula.  Thus we have the important result that when a discrete data sequence, , is proportional to samples of an underlying continuous function, , one can observe a periodic summation of the continuous Fourier transform, .  Note that any with the same discrete sample values produces the same DTFT  But under certain idealized conditions one can theoretically recover and exactly.  A sufficient condition for perfect recovery is that the non-zero portion of be confined to a known frequency interval of width .  When that interval is , the applicable reconstruction formula is the Whittaker–Shannon interpolation formula. This is a cornerstone in the foundation of digital signal processing.