Chess engines will have a Principal Variation (PV) that may be as many as 30 (or more) ply deep. Of course, the PV and the other facets of the engine help to determine the best move at the root position (the first ply).
However, how accurate is the rest of the PV? Some of the PV is most certainly wrong; for example, the very last ply of a depth 30 search will almost certainly change in evaluation if it were instead treated as the root position. Is there an easy way determine how much of the PV is trustworthy, and how trustworthy it is?