上图最后一行，mode=protect <br>
要是不设成保护模式，会怎么样？

OFFSET=(<n1><,n2>)<units > | (<n1<units>><,n2<units>>)
specifies the distance from the first and last major tick marks or bars to the ends of the axis line.

The value of (n1) is the distance from the beginning (origin) of the axis line to the first tick mark or middle of the first bar. The value of (n2) is the distance from the end of the axis line to the last tick mark or middle of the last bar.

On a horizontal axis, the (n1) offset is measured from the left end of the axis line and the (n2) offset is measured from the right end. On a vertical axis, the (n1) offset is measured up from the bottom of the axis line and the (n2) offset is measured down from the top of the line.

To specify the same offset for both n1 and n2, use one value, with or without a following comma. For example, either option sets both n1 and n2 to 4 centimeters:
offset=(4 cm)
offset=(4 cm,)

多谢！