DataItem.PreviousSample returns Current Sample

[MattCosturos]

Need to skip Count-2 instead of Count-1.
If you skip Count-1 you get to the end of the list and return a default (blank) sample

public DataItemSample PreviousSample { get { return _dataItemSamples.Skip(Math.Max(1, _dataItemSamples.Count - 2)).FirstOrDefault(); } }