Got one.
It's nice.
18% grey.
Works.
Good size.
Lives on my work ID lanyard.

I was almost sold but I really wanted 18.1% grey so....

Why 18% grey? *confused*

Your camera meter isn't terribly clever.
It'll calculate the exposure to render your subject as an 18% grey tone. If you meter off a piece of white cardboard, for example, the meter assumes you're looking at an 18% grey tone, and works out the exposure necessary to show that white cardboard as 18% grey. Which means that in print, your white card is going to be about 2 and a half stops out.
This means that if you metered off a piece of white paper, and it suggested 1/125 at f/8, you'd need to open the aperture up to between f/4 and f/2.5 to get the correct exposure.
And the opposite is true - if you're metering off a black wall or cloth, then it'll try to get that up to an 18% grey and before you know it, you're having to stop down 2 stops to correct it.
Unless, of course, you're reading off an 18% grey source, in which case you may as well be Rankin, Bailey or Adams.

Concur - except for the 18% grey bit. I use good old mother earth. She's available anytime, anywhere and can't be lost, which will happen to your spudz cloth because of that naff clip.

Al

PS have replaced said naff clip with aluminium carabiner type thingy

I haven't seen a spudz up close but I guess they use a plastic clip as it is less likely to scratch than a metal one.

Struggling to understand the difference between 18% grey, white, exposure and white balance. A thread on dpreview just confused me. Could anyone please elaborate in a "guide for dummies" fashion?

Digital cameras try to help you by averaging exposure to give nominally the best image. Pure white and pure black will generally tend to be averaged to grey by auto exposure.

By exposing manually on an 18% grey (or mother earth, as Al said), this averaging won't occur.

There's something I read a while ago about a Kodak misprint that meant the grey card should be 20%, not 18% as it is now.

White balance is simply telling the camera what white is. So for that, you use a nice sheet of plain white card. What 'white' is varies under different colours of light, so you can compensate to a degree in camera by pointing it at a white thing and using that as your white point, from which the camera works out how other colours will respond.

However, if you were to use the same card for an exposure reading, the camera effectively shifts that plain white card into an image with an overall 18% grey tone. So you'll end up being a couple of stops over. Using a darker, say black, colour to take your exposure reading from results in you needing to stop down a couple of stops.
The two things are separate and different.

Okay so think I'm starting to figure things out a little (have to do it bit by bit or my head will explode).

I've always set WB by using something white - typically a white sheet of A4 folded in half twice to provide an A6 "card", which I can then set the WB to.

So if I wanted to set the correct exposure, I use the camera's spot metering function, point it at a grey card (zoomed to fill the whole screen), and then lock it?
Then just fiddle with the aperture and shutter speed settings to take pics?

What about ETTR?

On a dive you can use the palm of your hand to set white balance.

^^^Yeah I saw that on dpreview as well. Apparently caucasians will have a slightly different grey value compared to non-caucasians.

Have you got a link for that review? I've never read anything on it, just picked up knowledge on the fin so to speak.

Wasn't an article - just some threads on the forum. I used "18 grey" site:dpreview.com and looked for some stuff.

Here are some links: clicky and clicky and clicky

HTH. I was reading it last night after watching American Dad, so my mind wouldn't be brilliant at comprehending it all. Will spend some time this weekend on it.

Cheers, didn't know about usage on land.