A quality control manager is inspecting four digital scales to see if they accurately reflect a weight of 0 ounces. The table shows the weight displayed on four empty scales.

Empty Scale Weight Displays
Scale 1
–1 ounce
Scale 2
–2 ounces
Scale 3
0 ounces
Scale 4
–1 ounce

What is the average error in the scale displays?
–4 ounces
–1 ounces
0 ounces
1 ounce