Steelkilt asked some good questions about the Citizen 800m (given the recent interest in vintage Citizen watches) and I thought they deserved some good answers. Here are some specs and some of my impressions on this watch. I apologize in advance for some of the photography - I'm still working on my lighting technique!
The watch is big - from end to end (including the "bump") it's a solid 50mm and including the crown at 8 o'clock it's a shade over 52mm. However, despite its size, being a Ti watch, it's extremely light and doesn't move around much when the wristband is done up. It's not a dress watch, though - it's a good 16mm deep and the aggressive look of the bezel suggests that it's built for action.
The hands and dial are all big no-nonsense indicators and very legible. The 60 click bezel is one directional and moves smoothly with a luminous index at 0. The bezel width itself is 42mm while the crystal is 38mm, so this is no dainty watch. Here it is on my own 7 3/4 inch wrist.
The example I got was in mint condition when I got it except for one flaw - the lume was totally gone. This isn't totally a surprise especially since the watch is about 14 years old. I have always been a fan of Citizen watches and their lume was great. The only solution was to send it to Jack at IWW who worked his usual magic on it. Now the watch is in pristine condition, it glows like a torch, and it's ready to dive or do anything.
At any rate, it's not a small watch but by the same token, it's not a mammoth. Although I've not seen a comparison with an 800m and a Tuna Can, I've tried to include some common watches as a point of reference so my fellow forumers can get a better idea of how big this watch is or isn't.
Aqualand Promaster and 800m
6105-8119 and 800m
Samurai and 800m
I haven't yet seen a comparison of the 800m with a 300m Ecozilla or a Tuna so I can't really comment as to the size difference with those watches.