At a certain time of day, every day, my clock appears to be an hour fast. At another time of day, it appears to be an hour slow. It is neither fast nor slow. What's wrong with it?
Maybe the hour hand isn't moving. If the minute hand is correct,
then it is arguably neither fast nor slow. But twice a day it
would appear to be exactly right, twice a day it would be appear to be
an hour fast, twice a day it would appear to be an hour slow. It
would also appear at other times to be two hours fast, three hours
Let's say (for example) the hour hand was stuck halfway between 2 and
3. Then it would appear to be correct at 2:30, an hour slow at
3:30, and an hour fast at 1:30. At 2 (and at most other times) it
would be obvious that something was wring, because the hour hand and
the minute hand would be inconsistent.