This should make it more clear. Now both fxn1 and fxn2 have series (M1, M2) and these are then passed through a LowPass filter (M3, M4). Why does M3 plot, but M4 is blank with -1?

var fxn1(var* Data,int Period) {
return (Data[0]-MidPoint(Data,Period))/(MaxVal(Data,Period)); }

var fxn2(var* Data,int Period) {
return (Data[0]-MidPoint(Data,Period))/(MaxVal(Data,Period)-MidPoint(Data,Period)); }

function run() {
StartDate = 2002;
LookBack=1440;
set(PLOTPRICE+PLOTNOW);
PlotBars = 20000;
var* Price = series(price());
vars M1=series(fxn1(Price,1440));
vars M2=series(fxn2(Price,1440));
vars M3=series(LowPass(M1,100));
vars M4=series(LowPass(M2,100));
plot("M1",M1[0],NEW,BLUE);
plot("M2",M2[0],NEW,BLUE);
plot("M3",M3[0],NEW,BLUE);
plot("M4",M4[0],NEW,BLUE); }