From the manual....
X-T2 (Version 2.10) Owner’s Manual: P 150 FOCUS BKT
Option Description - FOCUS BKT
The following settings are available when BKT SELECT is chosen for Z FOCUS BKT.
FRAMES - Choose the number of shots.
STEP - Choose the amount focus changes with each shot.
INTERVAL - Choose the interval between shots.
The relation between focus and the options chosen for FRAMES and STEP:
- Focus proceeds from the starting position toward infinity.
- Small STEP values translate to small changes in focus, larger values to larger changes.
- Regardless of the option chosen for FRAMES, shooting ends when focus reaches infinity.