1) density matrix description of 90x - t - 180y - t - acquire:

2) - Problem using GAMMA -

The error in measuring the 8 Hz coupling is approximately 0.1 Hz with a 0.1 ppm shift between A and B. It is approximately 1.8 Hz with a 0.01 ppm shift difference between A and B.

3) – comparison of product operator and density matrix treatment of I1xI2z – see 1 below

4) – density matrix representation of I1xI2x + I1yI2y – see 2 below.