Hi, here is one easy approach.
1) Right-click in your graph and select Smoother > Save Formula.
2) Look at the formula in the data table... it will have 2 "Spline Eval" pieces, one for each member in the group.... something like this:
![brady_brady_0-1621270494707.png brady_brady_0-1621270494707.png](https://community.jmp.com/t5/image/serverpage/image-id/32889i43545F439CCF6B5E/image-size/medium?v=v2&px=400)
3) Copy + paste each individual piece, so that it operates on all rows, not just rows belonging to a specific group, into a new formula column.
***** NOTE: this may involve extrapolation in your case, so heed the relevant interpretive cautions. Each formula will look something like this:
![brady_brady_3-1621271009019.png brady_brady_3-1621271009019.png](https://community.jmp.com/t5/image/serverpage/image-id/32892iB0D4FEFC7306A859/image-size/medium?v=v2&px=400)
This will produce something like the last 2 columns, which I've named Curve 1 and Curve 2, in your table:
![brady_brady_1-1621270787914.png brady_brady_1-1621270787914.png](https://community.jmp.com/t5/image/serverpage/image-id/32890i46885D3164B4BAF3/image-size/large?v=v2&px=999)
Next, compute the difference in these 2 columns, using a new formula column or a 1-click transform from within Graph Builder, and graph the difference column and the 2 formula columns you previously created vs. x, to view the results:
![brady_brady_2-1621270859471.png brady_brady_2-1621270859471.png](https://community.jmp.com/t5/image/serverpage/image-id/32891i0AE42EE570C234DE/image-size/large?v=v2&px=999)
I've attached a table with illustrative table scripts and formula columns.
Cheers,
Brady