Question regarding ship's bells (British Navy, Nelson Era)

I recently found a nice little app for my iPhone that serves two glorious purposes:
[ol]
[li]To educate this landlubber about the schedule of bells and watches used aboard 18th and 19th Century ships of the line; and[/li][li]To annoy people around me.[/li][/ol]

The app, simply called “Ship’s Bells”, causes one’s iPhone to mark the passage of each half-hour with the requisite number of chimes as per naval use. It’s not splashy and doesn’t have a lot of options, but its biggest selling point – as far as I was concerned – is that one could select the British system, which breaks up the four hour block from 16:00 to 20:00 into two separate “dog watches.” Being a Master & Commander geek, this represents a total nerdgasm.

The one fly in the ointment – or, more appropriately, weevil in the hardtack – comes at the end of the last dog watch. At 20:00 the app chimes a total of 8 times. Seeing as how this is fourth segment of a two hour watch, should it not be only 4 bells? I mean, it seems a bit odd that the sequence of bells for the two dog watches should be 1, 2, 3, 4, 1, 2, 3, 8.

My rudimentary research (read: too busy/lazy to search beyond Wikipedia) suggests that 4 bells at 20:00 should be expected. Any old salts or armchair Jack Tars know the answer?

My WAG is so that you’ll know you’re at the end of a whole cycle, i.e., to distinguish between a.m. and p.m.?

Looking through Wikipedia, it appears the originally the last dog watch had 5-6-7-8 bells. But after the Nore Mutiny, which used five bells as the signal for the uprising, the navy stopped ringing five bells, and switched to 1-2-3-8; not sure why 8 was kept but not 6 or 7, but I’d guess that keeping the end of the watch is more important than the middle.

I think that this system still exists today.

As an O’Brian fan you will be well aware that the Naval day starts at midday.

I have this question running in two different forums, and the responses seem pretty unanimous. Eight bells in the last dog watch it is.

My ignorance has been defeated.

On *that *topic, anyway.

I noted that the system had changed after the Nore Mutiny, but I hadn’t delved far enough as to learn the reasons why. Now it makes sense.