Slating / Boarding in the UK
In the UK unlike the US with scenes having letter attached. The UK identifies every shot as unique. Regardless of the scene the slate number will always go up for ever new shot / lens / action etc..
For example you may start with Scene 3 when you are shooting on day 1 and then go to scene 4 and then 7. This is how that would look if we did 3 shots / setups for each scene.
Scene 3 Slate 1
Scene 3 Slate 2
Scene 3 Slate 3
Scene 4 Slate 4
Scene 4 Slate 5
Scene 4 Slate 6
Scene 7 Slate 7
Scene 7 Slate 8
Scene 7 Slate 9
Giving each shot a unique ID is handy for editors because they can scan quickly to pick an individual shot instead of bunching scenes together.
Slating / Boarding in the US
The US style slating is a combo of letters and numbers to correlate to the shot you are on for any scene.
So whenever you move to a new scene in the script you would right that scene down and then for each setup / lens change in the scene you would add a letter and count up from A-Z.
Lets say we are on scene 3 and we have 4 shots, this is how it would look on the board:
Scene 3 - Master
Scene 3A - Mid
Scene 3B - Over the shoulder
Scene 3C - Over the other shoulder.
If you go through till Z then you go back to A and double up the letters, so the 27th setup/lens change for scene 3 would go as follows:
Scene 3AA
Scene 3AB
Scene 3AC
