Pioneer Dj DDJ-FLX10 4-Channel DJ Controller for rekordbox and Serato DJ Pro (Black) - Manual (Page 17)

Part names and functions
17
En
[SHIFT] + press:
Sets the deck as the master.
10 TEMPO slider
Adjusts the playing speed of the track.
11 KEY SYNC button
Press:
Changes the key of the track to match the other deck.
[SHIFT] + press:
Changes the key of the track that's playing to the original key.
12 TEMPO RESET button
Press:
Returns the playback speed to the original speed, regardless of the position of
the
[TEMPO] slider.
[SHIFT] + press:
Switches the range of the [TEMPO] slider each time the button is pressed
while holding the [SHIFT] button.
Switch between [±6%]  [±10%]  [±16%]  [WIDE]  [±6%] .
13 HOT CUE mode button
Press:
Enters Hot Cue mode.

Read more: Using Hot Cues (page 78)
[SHIFT] + press:
Enters Keyboard mode.

Read more: Using Keyboard mode (page 84)
14 PAD FX1 mode button
Press:
Enters Pad FX mode 1.

Read more: Using Pad FX (page 80)