The NMR Mosaic can help you keep from making mistakes!
If you happen to interpret a peak wrong, you will find that the Mosaic pieces you choose will not fit together. You should find the piece that fits the worst, because that is probably the one that was interpreted wrong. As an example, say someone put together these pieces for this spectrum.
But there is a problem when the pieces are put together. The second piece doesn’t match the third piece.
That means one of the two CH2 pieces is wrong. Re-examination of the spectrum shows the peak at 1.8 δ was a hextet, not a heptet. The correct piece has a CH3 and a CH2, not two CH3’s. After correcting the piece, all the parts match and show the molecule is 1-chlororpropane.