Nominals in DIMENSIONS keep changing!

Ok, I see where you're going now.
We do everything in DCC.
Most of our parts have a general location they go on the CMM. Set it up and Ctrl+q.
Otherwise, it's a read point or manual hit to show the CMM where to start.
The programs have a DCC 3-2-1 alignment at the beginning, to 'find' the part. Then on to the alignment proper.

In the grand scheme of things, does it really matter if the software is calculating and updating the Level plane before probing the Rotation?
In the end, the results should be the same if it probes all the features first, then does the math vs. resolving each one independently.

Yes, no, maybe......

Let's look at a test case (and this is one I USED to run into a lot, but since has been eliminated from our process) and this might be a little long too!

We have to do reverse engineering on details. Some of these details are VERY tall, they all have dowels in them. The relationship between the dowels is VERY important to make the detail right. So, since a tall detail is too tall to probe the dowels from the 'top', the detail has to be set on it's side (on risers). Unless you square that detail up to the machine axis, when you measure the plane on the bottom, then measure the lines on the side, the probe comp WILL be off for the manual alignment for those lines, IF you are just using the workplanes (which will be to machine axis). If you set the detail up so that the base is 30 degree out of sqaure to the machine axis, you will get 30 degrees of cosine error in the probe comp for those lines. However, if you probe the plane, THEN do just a level alignment to it, the workplanes will now be sqaure to the measured plane instead of to the machine and that cosine error will be gone. When they added the ability to use a feature for the workplane, this issue could be worked around. But, let's say you didn't know about the feature=workplane thing (or are using an old version that does not allow it). So, you probe the plane and 2 lines. The 2 lines have probe comp based upon maching work planes. The measured plane will have correct probe comp (it's a 3-D feature after all!), the lines will not (2-D features workplane dependant). BUT, following good programming, the DCC alignment will then correct for the cosine error from the manual alignment because you are now square to the plane as well as square to the lines (even if they are not correctly comped and thus off location by the cosine error). The DCC features correct for it. Do you follow what I am getting at? IF you follow correct manual-dcc alignment process, your manual errors will get corrected and it isn't an issue. BUT, some people think that you can't allow even the most minor error in the manual alignment, which, IMO, is not really required.

Ok, I see where you're going now.
We do everything in DCC.
Most of our parts have a general location they go on the CMM. Set it up and Ctrl+q.
Otherwise, it's a read point or manual hit to show the CMM where to start.
The programs have a DCC 3-2-1 alignment at the beginning, to 'find' the part. Then on to the alignment proper.

In the grand scheme of things, does it really matter if the software is calculating and updating the Level plane before probing the Rotation?
In the end, the results should be the same if it probes all the features first, then does the math vs. resolving each one independently.

Yes, no, maybe......

Let's look at a test case (and this is one I USED to run into a lot, but since has been eliminated from our process) and this might be a little long too!

We have to do reverse engineering on details. Some of these details are VERY tall, they all have dowels in them. The relationship between the dowels is VERY important to make the detail right. So, since a tall detail is too tall to probe the dowels from the 'top', the detail has to be set on it's side (on risers). Unless you square that detail up to the machine axis, when you measure the plane on the bottom, then measure the lines on the side, the probe comp WILL be off for the manual alignment for those lines, IF you are just using the workplanes (which will be to machine axis). If you set the detail up so that the base is 30 degree out of sqaure to the machine axis, you will get 30 degrees of cosine error in the probe comp for those lines. However, if you probe the plane, THEN do just a level alignment to it, the workplanes will now be sqaure to the measured plane instead of to the machine and that cosine error will be gone. When they added the ability to use a feature for the workplane, this issue could be worked around. But, let's say you didn't know about the feature=workplane thing (or are using an old version that does not allow it). So, you probe the plane and 2 lines. The 2 lines have probe comp based upon maching work planes. The measured plane will have correct probe comp (it's a 3-D feature after all!), the lines will not (2-D features workplane dependant). BUT, following good programming, the DCC alignment will then correct for the cosine error from the manual alignment because you are now square to the plane as well as square to the lines (even if they are not correctly comped and thus off location by the cosine error). The DCC features correct for it. Do you follow what I am getting at? IF you follow correct manual-dcc alignment process, your manual errors will get corrected and it isn't an issue. BUT, some people think that you can't allow even the most minor error in the manual alignment, which, IMO, is not really required.