The balance may not have been on a level surface, causing inaccurate readings.

You: ‘Emma did you check that the balance was level before we used it?’

Emma gestures toward the base of the balance. “I verified the balance was level before use. I remembered that this balance has a built-in spirit level, and I confirmed the bubble was centered. 

Dr Smith: ‘Well-done Emma! This step ensures accurate readings when the scale is perfectly horizontal. If it were off, you’d see the bubble shifted, indicating a tilt.” 

We still have two options to consider. Which is more likely?