Tripod spirit level - 2way or 3way

[dragonaxe]

Hi folks

I want to buy a hotshoe mounted spirit level (nice and cheap on ebay). There's ones with 2 chambers and ones with 3. Which is best? ... can't quite figure out the reason for the third bubble

[revi]

Well, a spirit level aligns in one direction, in 3D there are 3 directions, so ideally you need 3 chambers

All joking aside, with two levels, you can align the camera in landscape format (normal position), to get it level in the left/right direction (for a level horizon) and in the forward/backward direction (to keep parallel walls parallel in the image).
The 3rd comes in play when you turn the camera for portrait format shots (one of the chambers used in landscape format will end up vertical, so doesn't work anymore, the 3rd one takes over).

[dragonaxe]

DOH!! I didn't think of that! lol
Thanks Revi...a 3 way one it is then