The rule is to count the decks with complete rows of guns on them (unlike the forecasle and quarterdeck which have some guns). It should be easier on a frigate which only has one complete row of guns. Of course, it just so happens that they are on the 'upper deck'. The deck below, where the crew are berthed, has no guns but is called the 'gundeck'.

I was a bit disappointed when I visited Victory. As it is a RN ship in commission you get a guided tour from some serving sailor who just gives you the (often inaccurate) yarns of the sailing navy that have come down to the present navy. My guide was a Leading Seaman, Electronics Warfare Branch! At least there's that raised brass plaque that marks the place 'where Nelson fell', and you can do the joke about 'I'm not surprised, I nearly tripped over it myself'!

On the other hand, visiting Warrior was a treat. The guides are highly professional, dressed as petty officers of the period, and you get to wander about at leisure. The guides are placed at specific points and well able to answer questions about the ship and its restoration.