Hi Alison,
I was talking about the bench method that I was using as an example.
It is hard to see in the attached image but the rim should be kissing the packer when it is correct. In the image there is a gap of about 1.5mm. To lower the rim on to the packer loosen the upper nipples and tighten the lower ones this will drag the rim toward the packer.
If the rim becomes offset from the centre of the hub after a ride the best method is to leave the wheel on the bike and adjust the nipples to suit. To move the rim to the right loosen the nipples on the left and tighten the ones on the right. Do four at a time and work around the rim.
Ji