The mean absolute deviation is the sum of the differences between data values and the mean, divided by the count. In this case it is 15.7143

The differences are that when the earth's plates push together

The sum of two negative numbers is positive and the sum of two negatives is negative. If you have both positive and negative numbers the sum can be either so look at the absolute value. If the negative number has a greater absolute value, the sum is negative. If the positive number has a greater absolute value the sum is positive. If the absolute values are equal, the sum is zero.

If the negative has a greater absolute value, the sum will be negative.

If the positive has a greater absolute value, the sum will be positive.

The mean deviation or absolute mean deviation is the sum of the differences between data values and the mean, divided by the count. In this case the MAD is 6.