The controls shown above are used to set the lower x-axis limit.
If auto-scale lower x-limit is toggled, the minimum x-value of any of the curves in the plot will be used as minimum value. The edit window shows the current value, 10 Hz in this example. It is possible to type a new value, but remember to validate it by pressing Enter.
The controls are used for moving the lower limit in either left or right direction.