This is a question that recently appeared in the CNC Tech Talk forum on our website.
As you know, Fanuc controlled CNC machining centers use fixture offsets to assign program zero. You'll have at least six fixture offsets, though Fanuc provides an option to get more. For most applications, especially with machines that do not have a rotary device (indexer or rotary axis), six is more than enough.
When your machine has six fixture offsets, they are instated by a series of G codes, ranging from G54 for fixture offset number one through G59 for fixture offset number six.
In many applications, only one fixture offset is required - and if this is the case, we recommend using fixture offset number one (instated by G54). The reason why we recommend this that when you power up the machine, it automatically instates G54. That is, G54 is initialized. Should you forget to include a G54 in the program, the machine will still select the correct fixture offset.