为什么我不断出错#NUM！ 第一次运行该函数后，重新运行它时没有错误？

Question

I'm trying to do some simple maths calculation on some values in some columns in gsheet. Each value in each column is also populated from other sub functions prior to this function that kept giving me error #NUM! each time I run it but then it'll turn out to be ok with the correct expected output when I rerun it again.

The logic is supposed to be as below:-
Nett Total Item = Gross Total Item - Total Subtract Item + (Total AddVal * (Gross Total Item - Total Subtract Item)) + (Total MoreVal * (Gross Total Item - Total Subtract Item))

Below is my code :

const sheet=SpreadsheetApp.openById("1c0-vzYQA_9KVSiSgHUtS-3iBBGhTg3EcCZBm7rZDIpM").getSheetByName('mydata');
const lastrow=sheet.getLastRow();

function myFunction(){
  getGrossTotalItem(); //external fn to populate and setValue Gross Total Item in lastrow col AN
  getTotalSubtractItem(); //external fn to populate and setValue Total Subtract Item in lastrow col AV
  var TotalAddValrate=getTotalVal()[0]; //external fn to return % 1st val in the array and display in lastrow col AW
  var TotalMoreValrate=getTotalVal()[1]; //external fn to return % 2nd val in the array and display in lastrow col AX

  var grossTotalItem=sheet.getRange(lastrow,40).getValue();
  var totalSubtractItem=sheet.getRange(lastrow,48).getValue();
  var diff=grossTotalItem - totalSubtractItem;
  var TotalAddVal = TotalAddValrate * diff;
  var TotalMoreVal= TotalMoreValrate * diff;
  var nettTotalItem = diff + TotalAddVal + TotalMoreVal;
  sheet.getRange(lastrow,51).setValue(nettTotalItem);
}

It should be very straightforward process though but I don't understand why I keep getting the err on Nett Total Item until I run it the second time.
But all other values have no issue. Perhaps the process time to return the values for nettTotalItem formula to run is insufficient or something?
Appreciate if anyone can correct my code to calculate a better way or more efficient with no error.

I used Logger.log to capture the result as per advised by @Mario. it does shows that the desired output is there, but I just don't understand why is it not printed in the cell range as coded.

Answer 1

After tracing through the logs, I found the culprit was sets of scripts to populate the TotalAddValrate value in external fn getTotalVal() . Below was my original code :

function getTotalVal() {
  const paramdata=paramsheet.getDataRange().getValues();
  const data=sheet.getDataRange().getValues();
  
  var TotalAddValrate=data[lastrow-1][48];
  if(TotalAddValrate==''){
  var TotalAddValheader=data[0][48];
  var paramrow=paramdata.findIndex(TotalAddValrate=> {return TotalAddValrate[0] == TotalAddValheader }) +1;
  TotalAddValrate=sheet.getRange(lastrow,49).setValue(paramdata[paramrow-1][1]);
  }

  var TotalMoreValrate=data[lastrow-1][49];
  if(TotalMoreValrate==''){
  var TotalMoreValheader=data[0][49];
  var paramrow=paramdata.findIndex(TotalMoreValrate=> {return TotalMoreValrate[0] == TotalMoreValheader }) +1;
  TotalMoreValrate=sheet.getRange(lastrow,50).setValue(paramdata[paramrow-1][1]);
  }
  var allvals=[TotalAddValrate,TotalMoreValrate];
  return allvals;
}

The weird thing is the original sets of scripts to populate TotalAddValrate value was identical with the original sets of scripts to populate TotalMoreValrate value but somehow I don't see any issue on TotalMoreValrate scripts so I retain the code as it is. As for the TotalAddValrate scripts, I changed it to below and I finally got what I expected:-

  var TotalAddValrate=ordersheet.getRange(lastrow,49).getValue();
  if(TotalAddValrate==''){
  var TotalAddValheader=sheet.getRange(1,49).getValue();
  var paramrow=paramdata.findIndex(TotalAddValrate=> {return TotalAddValrate[0] == TotalAddValheader }) +1;
  sheet.getRange(lastrow,49).setValue(paramsheet.getRange(paramrow,2).getValue());
  TotalAddValrate=ordersheet.getRange(lastrow,49).getValue();
  }

Nevertheless, I would appreciate it so much if anyone can happily share any better and faster solution to get the same desired final output as per logic mentioned in my initial question. The one I've done is purely based on what I learned so far on GAS and I'm just starting about 2months ago.