把通达信自带指标“bb”今天的值减去昨天的值

我是菜鸟，不懂怎样把今天bb的值减去昨天的值。感谢大虾帮忙！ （如：今天bb：5.1 昨天bb：7.8 差就是-2.7） 附：通达信自带指标：bb N:=20; MID:=MA(C,N); VART1:=POW((C-MID),2); VART2:=MA(VART1,N); VART3:=SQRT(VART2); UPPER:=MID+2*VART3; LOWER:=MID-2*VART3; BOLL:=REF(MID,1); UB:=REF(UPPER,1); LB:=REF(LOWER,1); LOWER1:=MID-VART3; LB1:=REF(LOWER1,1); BB:(C-LB1)/(UB-LB)*100; MA6:MA(BB,6); 0;

爱约股解答：

N:=20;

MID:=MA(C,N);

VART1:=POW((C-MID),2);

VART2:=MA(VART1,N);

VART3:=SQRT(VART2);

UPPER:=MID+2*VART3;

LOWER:=MID-2*VART3;

BOLL:=REF(MID,1);

UB:=REF(UPPER,1);

LB:=REF(LOWER,1);

LOWER1:=MID-VART3;

LB1:=REF(LOWER1,1);

BB:(C-LB1)/(UB-LB)*100;

MA6:MA(BB,6);

0;

CZ:BB-REF(BB,1),NODRAW;