To hopefully clarify the above a little:
a) The machine must remain in its home position whilst step 4 is performed.
b) Say you want Work zero to be at machine coordinates (x, y, z). To achieve this, you could enter the values x, y and z directly into the Fixture offsets table. Alternatively, using the above method, you could enter the values -x, -y and -z into the dros at step 4. The magnitudes of the numbers are the same in each case, but the signs differ. This arises because the Fixture offsets table contains the machine coordinates that correspond to Work sero, whereas at step 4 you are entering the Work coordinates that correspond to Machine sero.
Allan