function onEdit()
{
  //use the currently open sheet
  var sheet = SpreadsheetApp.getActiveSheet();

  //set the cells for increase/decrease/total
  var total1 = sheet.getRange("C2");
  var increase1 = sheet.getRange("C4");
  var decrease1 = sheet.getRange("C6");
  //get the current value of "total"
  var total1num = total1.getValue();
  //if "increase" was changed, calculate new "total" and set cells
  if (increase1.getValue() !== "")
  {
    total1num = total1num + increase1.getValue();
    total1.setValue(total1num);
    increase1.setValue("");
  }
  //if "decrease" was changed, calculate new "total" and set cells
  if (decrease1.getValue() !== "")
  {
    total1num = total1num - decrease1.getValue();
    total1.setValue(total1num);
    decrease1.setValue("");
  }
}