刚才我用passwd大哥的方法做出来了。以下为做法：做一个按钮，程序如下：
int f;

f=GetPropWord("NewPdl1.PDL","Trend","TimeRangeFactor")-1; //Return-Type: BOOL
SetPropWord("NewPdl1.PDL","Trend","TimeRangeFactor",f); //Return-Type: BOOL

NewPdl1.PDL 为趋势图所在的画面名称，
Trend 为趋势那个控件的名称

逆变如下：
int f;

f=GetPropWord("NewPdl1.PDL","Trend","TimeRangeFactor")+1; //Return-Type: BOOL
SetPropWord("NewPdl1.PDL","Trend","TimeRangeFactor",f); //Return-Type: BOOL

在此特地谢谢passwd大哥