Big timing differences on wrist vs off: normal?

[the dark knight]

Something I just noticed recently on my Sub. On the wrist, the watch gains quite a bit. I'd say almost a full second/hour. Off the wrist, dial up, it almost seems to lose about the same rate.

Over a day, I'm split almost even on wrist/off, since I don't wear it to sleep, randomly take it off during day. So over 24 hours, seems to come in at about +5sec, which is within COSC specs and totally ok with me.

Doesn't bother me personally, but wondering if this is any kind of indication of an issue that might need servicing?