local dx = (1/2) * (4.84 - 1.76) / 79
local dy = (1/2) * (41 - 12) / 79

gen id = _n

expand 6
sort id

by id: replace wt  = wt  - `dx' if _n==1
by id: replace mpg = mpg - `dy' if _n<=2

by id: replace wt  = wt  + `dx' if _n==2 | _n==3

by id: replace mpg = mpg + `dy' if _n==3 | _n==4

by id: replace wt  = wt  - `dx' if _n==4

by id: replace wt  = wt  - `dx' if _n==5
by id: replace mpg = mpg - `dy' if _n==5

by id: replace wt  = .          if _n==6
by id: replace mpg = .          if _n==6