如何取20日內最高、最低DIF值

我寫了下面的腳本，但無法使用，取不出最高、最低DIF

請幫我檢查，謝謝

// XQ: MACD指標

//

input: FastLength(12), SlowLength(26), MACDLength(9);

variable: price(0);

SetInputName(1, "DIF短天數");

SetInputName(2, "DIF長天數");

SetInputName(3, "MACD天數");

price = WeightedClose();

Value1 = XAverage(price, FastLength) - XAverage(price, SlowLength);

Value2 = XAverage(Value1, MACDLength) ;

Value3 = Value1 - Value2 ;

// 前面區段資料變動較大, 先不繪出

//

if CurrentBar <= SlowLength then

begin

Value1 = 0;

Value2 = 0;

Value3 = 0;

end;

Plot1(Value1, "DIF");

Plot2(Value2, "MACD");

Plot3(Value3, "Osc");

input:Length(20,"天期");

value4=Highest(Value1,Length) ;

value5=lowest(Value1,Length) ;

plot4(value4 , "最大DIF"); 

plot5(value5 , "最小DIF");