How to define the column/row/range where the script should start

In column Q start at row 15 is dynamic cell which goes down the column and contains a %-Nr.Next to it in column R i want to show the recorded max value per row. During my research i found here this code snipped which is where i was looking for.

Answer

function recordMax() {  var sheet = SpreadsheetApp.getActiveSheet();  var range = sheet.getRange("A1:B1");  var values = range.getValues()[0];  range.setValues([[values[0], Math.max(values[0], values[1])]]);} 

Now i tried to fit this to my sheet and changed it to onEdit for autoupdate.Also i wanted to change the Range "A1:B1" to my Q:R start at row 15.This is how far i came and didn't work

var mainWsName = "WATCHLIST AKTIEN";var ws = SpreadsheetApp.getActiveSpreadsheet().getSheetByName(mainWsName);function onEdit(e) {  var activeCell = e.range; // Here i run into the Error - Cannot read property 'range'  var r = activeCell.getRow();  var c = activeCell.getColumn();  var wsName = activeCell.getSheet().getName();  if(wsName == mainWsName && c == 18 && r > 14){ // start in Q15 Nr. to recordMax. show Max in R15  var range = ws.getRange(r, 18,1,2);  var values = range.getValues()[0];  range.setValues([[values[0], Math.max(values[0], values[1])]]);  }}

Also it should set back to 0 when cell B2 is emptyI guess i would implement another IF something like this

if(wsName == mainWsName && ws.getRange(r,2).getValue()==''){    ws.getRange(r, 18,1,2).clearContent();