把low<low55换成crossover（low,low55），图表上不出信号了，不知道是什么情况？求高手解答。

High10=Highest(High[1],length4);
            High55=Highest(High[1],length12);
            low10=Lowest(Low[1],length4);
            low55=Lowest(Low[1],length12);

BuyCondition1=CrossOver(High,MA1);

SellCondition1=CrossUnder(Low,MA1);

BuyCondition2=CrossOver(High,High10);
            SellCondition2=CrossUnder(Low,Low10);
            BuyCondition3=CrossOver(High,High55);
            SellCondition3=CrossUnder(Low,Low55);