Wonderful example. For several years I taught at a convention where we used (in each class or event) the same model machine and the appropriate 1/4" foot that came with the machine and the same 1/4" button on the machine. None adjusted the same. We spent time at the beginning of the class calibrating the stitch width. So....proved that all machines and feet were not the same.
Therefore, some rules (if I can use that term) Always calibrate or adjust your seam allowance before beginning the sewing and make a test piece to be sure and then USE THE SAME machine for the entire project and never assume the measurement will continue throughout the projejct. For accurate work it is necessary to check and correct as the project goes along.
I took a class with Sally Collins recently. She is consider to be the master of accurate minitiature piecing. She said that the work is only as good as the last seam sewed. So make a section and then measure it and correct if necessary.

all 3 of my 1/4" feet require moving of the needle..
same machine,
different settings to get the right seam allowance.
i have the Janome 6600.

i also have the jem, which the snap on feet are interchangable, and it requires a different setting!
i try to start and finish piecing on the same machine..
or try to remember to check the seam allowance every time i start the machine up!

Sooooooo, what you are telling me is:
In these two sets of blocks you have 8 seams each.
The longer set 'seam' is the width of a thread larger than the smaller set.
So laying 8 pieces of thread side by side is how much bigger the larger set is than the smaller set?
This was an excellent visual. It will be burned in my mind forever because you showed it to me this way.
Thank-you. All of the examples and information in this post and the responses is very helpful to me.

Thank you--I'd have never thought of this. You've saved lots of us time and aggravation (and hair-pulling!).

I DID THE SAME EXACT THING - sewed on one machine at class and then followed up on another machine at home.

UGGGHHHH had to undo both 6 FOOT sections I finished.

I also learned the hard way with log cabin blocks. Half made on one machine the other on a different machine. I now tell all my students when you start a quilt on one machine, make ALL the blocks on THAT machine.
Out of three machines I use, I get a different seam allowance when attaching binding with my walking foot.

You are so right. I also found out all rulers are not the same. I try to use the same ruler for a quilt. This helps explain why all blocks we receive in exchanges are not always the same size. It can be very frustrating, can't it.

Well now I know that I am not crazy. I told the shop where I purchased my machine that the 1/4 inch foot does not sew 1/4 inch seams. They told me that I was crazy and it definitely does. Hmmmmm thanks for letting me know that I was right.

great tip.

I participate in block exchanges and was always frustrated that MY blocks weren't coming out to the right size, couldn't really get them square, ect. I finally decided to select blocks that I could piece a little large and use the 12 1/2" square ruler.

Since then I am happier, still struggle to get the exchange blocks to go together, but have learned to add sashing, accept the blocks as they were intended, a gracious act of generosity and community and put them together and enjoy my quilts.