Can the calculations of these two steps be modified to be completed in one step?

[#1]

Thanks Experts!

dt=Open("$SAMPLE_DATA/Big Class.jmp");
ca="A";If(Is Missing(Try(Column(ca)<<Get Name)),New Column(ca));Column(ca)<<Formula( if(height>=lag(height,1),weight) );Current Data Table()<<run formulas;Column(ca)<<deleteFormula;
ca="B";If(Is Missing(Try(Column(ca)<<Get Name)),New Column(ca));Column(ca)<<Formula( if(height<lag(height,1),weight) );Current Data Table()<<run formulas;Column(ca)<<deleteFormula;
ca="C";If(Is Missing(Try(Column(ca)<<Get Name)),New Column(ca));Column(ca)<<Formula( if(row()>9,round(sum(A[Index(Row()-9,Row())])/sum(B[Index(Row()-9,Row())]),2) ));Current Data Table()<<run formulas;Column(ca)<<deleteFormula;

ca="D";If(Is Missing(Try(Column(ca)<<Get Name)),New Column(ca));Column(ca)<<Formula(  if(row()>9,sum(weight[Index(Row()-9,Row())]&height[Index(Row()-9,Row())]>=height[Index(Row()-10,Row()-1)])/sum(weight[Index(Row()-9,Row())]&height[Index(Row()-9,Row())]<height[Index(Row()-10,Row()-1)])) );Current Data Table()<<run formulas;Column(ca)<<deleteFormula;

[#2]

(assuming your goal is either speed, or easier to read code...)

Column formulas are not magic. They are not faster than JSL. They are JSL.

OK, they can be a little bit magic; JMP's engine that evaluates columns does figure out which columns are dependent on other columns and evaluate the not-dependent formulas first. But that never happens here since the formulas are deleted.

Since you are creating / running / deleting the formula to populate a column, four times, you might want to try a single JSL loop with the four inner statements inside. Be sure to use the <<beginDataUpdate before the loop and <<endDataUpdate after the loop. I don't expect this to be a lot faster, but it might be a lot easier to read. (Your example has some repeated computations that could be streamlined in a single loop.) You can probably use ForEachRow(dt, ... ) and get the same looping speed that <<runformulas has.

[#3]

none of the weights is empty.

weight[Index(Row()-9,Row())]&height[Index(Row()-9,Row())]>=height[Index(Row()-10,Row()-1)]

can be reduced to 
height[Index(Row()-9,Row())]>=height[Index(Row()-10,Row()-1)]

or maybe: you wanted to calculate something else?

selection of A & B.
comparison of C&D

let's challenge it:
a)

weight[11] = 500;

b)

current data table()<< add rows(10);
height[41::50] = 70;
weight[41::50] = 1;

[#4]

I need this form composed of several formulas and don't want any loops in it.
Thanks Experts!

aaa="";
current data table(dt);Eval(Parse("Column(dt,\!"ABC\!")<<Formula("||aaa||")"));dt<<run formulas;Column("ABC")<<deleteFormula;s=N Rows(Loc(dt[0,"ABC"]>0));