把low<low55换成crossover（low,low55），图表上不出信号了

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);