The average of its errors is 0- ie it is not biased. Ofc, the average absolute error, which in English one could very reasonably refer to as "average error" is much greater than 0.
That may technically be correct, but it is incorrect in the real world. I submit that error is error in the real world. Mathematics can go jump off a cliff unless it wants to be helpful. :)
"If clocks rounded to the nearest minute instead of truncating, the average error would be 0.”
The negative and the positive error don’t cancel each other out. They are both error. The absolute value needs to be used.