You and your lab partner, Mel, are engrossed in a chemistry activity using beans to compute the average atomic mass of an element "beanium". You have three isotopes of beanium to measure. Using a triple beam balance, you find the mass of each isotope three times and then take an average. You and Mel compute an average mass for beanium of 8.93 grams and your percent error is 18%. Your teacher instructs you to try again and you end up with the same results. In fact, no matter how many times you try, your percent error is between 18 - 20%.

What is the MOST LIKELY source of error in this activity?

A) random error: Mel misreads the balance occassionally.
B) random error: You and Mel take turns reading the balance and do not read it to the same accuracy.
C) systematic error: The balance is not calibrated accurately, resulting in inaccurate measurements.
D) systematic error: Every now and then you or Mel stop to chat with your neighbors and lose track of what you are doing.