Am I evaluating the position correctly?

[[Ca...]]

ASME. I have a position output but changes whether I use base alignment or input individual datum.

 

Edited November 14, 2025

[[Ma...]]

Hello,

try to make a projection of 3d-line  on Plane A and use it instead of 3d-line on base allignment , and see if change something.

[[Ma...]]

I wonder if Circle B is in Z=0 or not. If not than it would imply this difference.

Can you post Circle B window as you did for Circle 37.

For comparing values you should have set tangential element on those circles.

[[Ca...]]

Projection and 3d line make no differences.  Evaluation on datums is default to outer tangential. Datum B is a bolt circle of eight holes. 

[[Ky...]]

It is hard to say without having the program in hand, but the difference is likely caused by evaluations. The base alignment DOES NOT respect the settings in the measurement menu. The features, unless you go in and edit them, will be LSQ and not constrained as the setting says (as it should, the base alignment is meant for finding the part reliably to measure, not to evaluate the results). So, the base alignment and putting in the datums individually ARE NOT the same thing, at least by default.

 

Additionally, even though the tertiary datum is not entered, I believe the old GD&T engine constrains things like this to the base alignment if it isn't given a tertiary. There are ways around that, but I do think as shown, the TP callout is over constrained.

[[Ca...]]

Filled out the tertiary datum. I'm trying to find out the X and Y measured coordinate of circle37 for position to be 0.587.  If I calculate the  𝑇𝑟𝑢𝑒𝑃𝑜𝑠𝑖𝑡𝑖𝑜𝑛=(𝑋2𝑣𝑎𝑟+𝑌2𝑣𝑎𝑟)×2. I get 0.253 and not 0.587

Edited November 17, 2025

[[Ra...]]

Enable the display banners for characteristics under Results Presentation through the CAD dropdown.

Highlight your position characteristic, and you'll see a banner like the box on the right. It's not intuitive, at least in 2022, but if it's an XY position, the first actual is X, second is Y. You can compare the position actuals for x and y versus the feature actuals. Might help you narrow down what's happening.

 

Or turn on "additional report" in the character settings editor. 

[[Ri...]]

I think you are getting all of this confused because you are hopping around menus, and looking at the data in three different ways. 

Like Kyle said, the Base Alignment does not abide by the rules you have set in the Measurement Setting (ISO 5459, and Outer Tangential). Later versions of Calypso do allow you to turn on the ISO 5459 for coordinate systems, but that isn't the case for you. 

So your Base Alignment is most likely not using ISO 5459, and most likely has the feature evaluation set to Gaussian. 

Your feature is measured inside of the Base Alignment, which is why the deviations inside of the Feature and the Position if measured to the Base Alignment are 1:1. 

Now, when you create the Position and build your DRF manually, it is going to use Outer Tangential for the Datums, and ISO 5459 constraints, which is why your results aren't 1:1. 

You can always right-click on the Datums inside of the Position and change them back to Gaussian, and turn off ISO 5459. 

Edited November 17, 2025

[[Ca...]]

Ok that makes sense.  Randawgg, that is what I'm looking for, the display banners shows the actual X and Y that is use to calculate the 0.587 position.

Just curious why positioning the datum back to itself wouldn't yield 0. Thank you everybody

Edited November 17, 2025

[[Ma...]]

I still think you have mixed tangential element and gauss - aka i think Circle B in datums is used tangential, but feature itself is gauss

[[Ca...]]

You're right Martin, the datum evaluate as tangential while the feature set to LSQ.

[[Pe...]]

Wouldn't the large of a form/sigma on Circle B cause a lot of issues?  It looks to me like the datum is very far out of round.

[[Ca...]]

The datum B is created from a bolt circle of eight individual holes. The part is large with warpage issue so the eight holes are not perfectly equal distance

[[Pa...]]

Rule #1 in my lab:

Don't ever use a base alignment as a DRF.  As you're reading there are lots of ways it can mislead you.

[[Ky...]]

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I agree with this sentiment 100%. Using the base alignment to compare answers is something we see on the phone support line all the time and I always tell customers that they aren't using the base alignment as intended. It is a complete apples to oranges comparison.

[[To...]]

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I would think Calypso would default to empty Primary, Secondary and Tertiary windows and not auto-populate with Base Alignment.  How many users think "I created my BA using the DRF, I  must be all set."

Edited April 6

[[RP...]]

2 years ago during my first year as a programmer, I was under the impression that the DRF should be the BA if possible.

Just recently I switched my method to relying on secondary alignments rather than all the characteristics under the base alignment.

[[DW...]]

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 It took me awhile to be able to articulate to bosses and peers what the base alignment was exactly, and how it doesn't have anything to do with DRFs. For any new guys reading this - the base alignment defines how the part is oriented and positioned in space for stylus navigation by establishing a coordinate system. The end. 🙂