This is because there is a misprint of the instruction. To activate or deactivate the summer time (daylight saving time), follow the below steps.
- The clock must be in the summer period time in order for this function to work.
- Press and hold both SUMMER TIME and CLOCK buttons for a short while.
- SUMMER TIME indicator will appears in the display and the time indication changes to the summer time (daylight saving time).
- To deactivate, proceed with Step 2.