Horizontal accuracy of anchors

I have some problems with the horizontal accuracy of anchors in interpolations from hairline to regular.
As you can see, the anchor is placed at the beginning of the t, but in thin styles, it does not work as expected.( I have rounded all coordinates.) Do you have any hints, what goes wrong here?

result:
image

image

I don’t fully understand your screenshots and what you are trying to do. But I suspect it to be a rounding error.

Why are you splitting the t in two pieces?

I have different tops for ligatures.

So, rounding errors occur even with anchors? And there is nothing, what I can do to prevent it?

Move the t-top part so that the “_t” anchor is at the exact same “x” position as the “t” anchor.

Ahhhhh! Great. Thanks al lot!

Yes. Same numbers are rounded the same way. Different numbers cannot possibly be rounded the same way.