I observed a few things as I was going through the trials. There was not a third option. Had I found a third option to choose if the lines were the same, I would have been more confused. However, I did sometimes have to stop and pause and see if one was really bigger than the other and at times it was easy to judge both lines.
What this lab reminded me of was being in an optometrist’s office and getting an eye exam where one has to choose between options “1” and “2” and how the doctor asks you to make a choice. In an eye exam, sometimes you get a third option of “about the same,” but here there were only two choices. Sometimes it may be that third response that complicates matters.