A word on grades...
Bouldering grades, and climbing grades in general, are the source of endless arguments and strife. It's a subjective system, and one person's idea of hard can be very different to another's - particularly if one is short and one is tall, or one is ultra-skinny and the other heavy.
We think that giving bouldering problems grades is a great way to point you in the right direction in terms of which climbs at the centre you might enjoy, and give you a sense of improvement over time - but grades aren't everything. The important thing is to have fun and enjoy your climbing - your sense of achievement having managed to climb something that you found a challenge is what really counts.
There are several different grading systems in use across the world. We prefer the Fontainebleau system, which is also popular in the UK (including on the Southern Sandstone - the nearest natural bouldering to Brighton, near Tunbridge Wells). This gives a number and a letter to indicate how hard the climb is, for instance 6A. Grade 6B would be one grade harder, 5C one grade easier.
The Font system starts at 1 for the easiest climb imaginable and goes all the way up to 8C+ for the super-humanly hard (only a handful of people in the world can climb at this level). It sounds complicated but isn't really once you get used to it. If you're used to a different system you can get a rough idea of how the Font system compares using conversion charts like the one here.