First point correction involves  scaling the initial point of an FID to correct for delays in acquisition. If there’s no acquisition delay (meaning that no first-order phase correction is required) then the first point truly reflects the area of the FID at time=0. If there is a delay (requiring first-order phase correction) the effective starting point has changed meaning that the first point doesn’t represent the full area at time=0 and so should not be scaled down. Choosing the correct first point correction will avoid issues with the baseline of the transformed spectrum

This can be done in NMRPipe using the command APOD with the -c flag.

So where there is little or no delay before acquisition the command would be nmrPipe -fn apod -c 0.5 and the P1 value should be approximately zero. This will correct for the double counting of the first point during discrete Fourier Transform.

Where there is a delay prior to acquisition and so P1 value is not close to zero, the command is nmrPipe -fn apod -c 0.5 ensuring that the first point is not scaled down.

Next: Apodisation