请教macd背离里面一些语句的理解

Params Numeric n1(10); Numeric n2(20); Numeric FastLength(12); Numeric SlowLength(26); Numeric MACDLength(9); Vars bool golden(false); bool ending(false); Series<Numeric> MACDDiff; Numeric AvgMACD; Numeric MACDValue; series<Numeric> ma1; series<Numeric> ma2; series<Numeric> DMA; series<Numeric> new_h; series<Numeric> new_ref_1_h; series<Numeric> new_l; series<Numeric> new_ref_1_l; series<Numeric> tem_new_h; series<Numeric> tem_new_h1; series<Numeric> tem_new_l; series<Numeric> tem_macd_l; series<Numeric> tem_macd_h; series<Numeric> macd_l; series<Numeric> macd_ref_1_l; series<Numeric> macd_h; series<Numeric> macd_ref_1_h; Events OnBar(ArrayRef<Integer> indexs) { Range[0:DataSourceSize() - 1] { MACDDiff = XAverage( Close, FastLength ) - XAverage( Close, SlowLength ) ; AvgMACD = XAverage(MACDDiff,MACDLength); MACDValue = MACDDiff - AvgMACD; //PlotNumeric("MACDDiff",MACDDiff); //PlotNumeric("MACDDEA",AvgMACD); ma1 = XAverage(close,n1); ma2 = XAverage(Close,n2); golden = CrossOver(ma1,ma2); ending = CrossUnder(ma1,ma2); DMA = ma1[5]; PlotNumeric("ma1",ma1); PlotNumeric("ma2",ma2); tem_new_l = lowest( l[1],nthcon(ending,0)); tem_new_h1 = highest(h,nthcon(golden,0)); tem_new_h = highest(h[1],nthcon(golden,0)); 请问用这个nthcon函数，在赋值给临时变量时，例如最后三行，取最高最低值时，用了前一周期，我不懂为什么不能用最新值，逻辑上理不过来，画图后也不是很理解，请指教，谢谢