OLL37 (Fish shape)

(F R’ F’ R) (U R U’ R’) (Fish shape head at left back corner)

r2′ D’ (r U’ r’) D (r U r) (Fish shape head at front right corner)

There are many algorithms which have D…D’ or D’…D pattern. For the most of the case, D’ comes after R’ turn, and D comes after R turn.

So, after you turn the rightmost slice of the cube toward you, you should move the bottom one backward by left ring finger. And vice versa for the latter case.

I think this is because the algorithm wants to keep aside UFR piece at the front or back left bottom corner while some operations of R-slice.

If you move R’ and D instead of D’, UFR piece goes to right back corner, and any R-slice move will affect it.

To avoid wrong turns, I try to avoid the algorithms of the reverse case (D comes after R’ turn, and D’ comes after R turn), if there are.