Secondary alignments vs. manual input of datums

[[Jo...]]

I've heard many points to be made when it comes to creating secondary alignments and using those in the datum reference window for features of form/location, vs. manually plugging in your datums in the primary, secondary and tertiary boxes. Just doing a quick and dirty comparison between the two usually will yield small changes out in the 5th-6th decimal place, that can probably be chalked up to differences in evaluation settings that I didn't bother to ensure matched completely on the characteristics side. There have been a couple instances where it changed the result enough to matter.
I've also had different people that work for Zeiss advocate that one way is best practice, and another would tell me the opposite, and yet another would say that it doesn't matter...

Anyone have a preference, or information on what *really* is the better way and specifically why? I always have assumed Calypso would properly constrain degrees of freedom based on plugging in your datums directly, provided the programmer has done their due diligence to make sure everything makes sense.

[[Mi...]]

*assuming ASME*

Using Secondary alignments is fine if:

You input your features correctly.
Set all features evaluation to the right setting, usually OTE
Activate "Form datum as per ISO 5459" under the constraint tab.

By default secondary alignments are LSQ and are not Formed as per ISO 5459, but DRFs are - if your copy of calypso is configured properly.

It's less work to just fill out the DRF properly, you can rotate them just like secondary alignments, and you can save them to reuse if that applies to your program.

Sometimes you have no choice but to use a Secondary alignment, as in the case of a profile callout with an incomplete DRF where you then use a Geometry Best-Fit alignment, if you don't have Curve. The Geometry best-fit needs a properly setup secondary alignment to reference.

[[Jo...]]

This is all basically what "my" method is also. I usually only use secondary alignments for GBF alignments like you mentioned, or sometimes I will use it to pull from the dropdown on the feature itself as a reference check if I want to make sure my nominals make sense, for example if there are rotated views on a print and my base alignment is such that I can't easily figure it out just by looking at the XYZs.

[[Me...]]

I Typically only used secondary Alignments to check angled geometry and make sure the basics match up. Otherwise i usually always manually selection them. Manually gives you the option to change evaluation settings (Inner/Outer Tangential/LSQ) which i usually changed depending if its an ID or OD